Talk:Logic/Archive 1

Archive-1 created Charles Stewart 07:44, 10 Nov 2004 (UTC)

Cut starts here
I took the liberty of removing some of the older entries from before 2004, and the ones that were irrelevent to the article, in part to try and make this page less than 32 kb. This page could benefit greatly from an explanation of how logic relates to artificial languages, predicate, sentential and modal logic as prime examples. This would also naturally involve a small digression on how logic relates to natural languages and linguistics in general, including say informal versus formal methods, and how natural deduction can be used to infer rules of inference.

Stuff
Why does compound sentence redirect to logic?
 * Seems to be a big mess of changing double redirects, I'll try to sort it out. Thanks for pointing that out &mdash; siro  &chi;  o  04:52, Sep 8, 2004 (UTC)

Who invented truth tables, Charles Pierce or Wittgenstein? Who should get the credit?

Shouldn't this page include the basic logic relationships? Why don't you add them to truth tables, connective, and quantifier?

Also the logic of relations, or polyadic quantification, which Quine said is what brought serious stature to logic as a field. It might also be nice if there were a striking & concise way to characterize the difference between formal or mathematical logic, & algebra (as the theory of calculation), i.e., the heart of the difference between formal reasoning & calculation, as opposed to lists of respective subfields.

A Calculus Of Ignorance?
Thinking about statistics and the frequentist formulation of confidence intervals ( The population parameter is "fixed but unknown") leads me to wonder if anyone has ever put the idea that something in a mathematical problem can be "given to be unknown" on a rigorous logical footing. Suppose we have an a symbol p representing a a "quantity" in a mathematical problem, be it a statistical problem or otherwise. Some examples of thethings that we might be "given" about p are:

1. p is an unknown number.

2. p is a normally distributed random variable with mean 0 and std. dev.= 1

3. p is a normally distributed random variable with unknown mean and std. dev.= 1

4. p is a normally distributed random variable with unknown mean and unknown std. dev.

5. p is selected by a person who has flipped a fair coin. If the coin landed heads then he chose p to be an unknown but fixed number. Otherwise p was chosen from a normal distribution with mean 0 and std. dev. 1. How the coin landed is unknown. (i.e. There is a 0.5 probability that p is "fixed but unknown" )

Lacking such a calculus, I, nevertheless attempt the following deductions:

If we are given 1) alone then an example of a valid conclusion is "The probability that p = 23.2 is either 1 or 0" (this follows famous textbook examples from statistics). If we are given 2) alone then the previous conclusion is invalid. If we are given 3) alone then we may say "The probability that {the probability that p = 23.2 is either 0 or 1} is 0". If we are given 5) alone then I don't think the previous conclusion is valid. I'm sure these examples suggest even more mind boggling ones that make the frequentist assumption look like simplicity itself. Has some obscure branch of logic worked all this out for us? (I'm not talking about Bayesian statistics, which involves adding additional assumptions.)

Stephen Tashiro

Domain Theory
Dana Scott's theory of domains should handle the above kinds of uncertainty to your satisfaction. The essential idea is that it is a kind of theory of types that is naturally related to a logic without the principle of excluded middle. Chalst 23:43, 11 Aug 2004 (UTC)

Law of identity
Should not the logic page include the Law of Identity as one of the three laws of classical logic? That is: A is A or A = A. It seems to me that this law of Identity is crucial to the application of the Law of Non-Contracdictories and the Law of Excluded Middle in determining the truth or error of a proposition. Afterall, Logic really is the mechanism by which we pursue truth and distinguish it from error.

Perhaps the three laws of logic could be more understandable to those who are not aquainted with them as follows:

Law of Identity: A is A, or A = A. Something (a proposition or a thing) is what it is. Example: An apple is an apple. However, all apples are not identical, and any particular apple is not any other particular apple. Stating the law is not without difficulty. For example, a paricular apple is only a single example within the broad spectrum of the class concept of "apple-ness." In this case, the law of identity is valid in making the detemination that, "this particular apple is an example of what is subsummed under the class concept of "apple-ness.""

Law of Non Contradiction: A is not non-A. Something is what it is and not what it is not. Example: Applying the Law of Identity, an apple is an apple. Then applying the Law of Non-Contradiction, an apple is not anything an apple is not. The law does not preclude the possibility that an apple could become something else, applesauce, for instance, but that an apple cannot be an apple and applesauce at the same time.

Law of Excluded Middle: A is B or non-B. Usually, when considering propositions, the Law of Excluded Middle is applied by stating that the proposition P is either true or false, with no third possibility (tertium quid) allowed. However, in keeping with our "apple" example in explaining the first two laws, we could state that, "an apple is either a fruit or a non-fruit (a vegetable, or an animal)"

It seems that the application of the laws as given in the examples above have a direct bearing on what the could be considered "significant speech" and in resolving the ever present problem of communicating propositions "meaningfully" by addressing the "one within the many."

The communication of a proposition "meaningfully" from one person to another is absolutely dependent upon the definitions of the terms in the minds of both. Since we've been using "apples" in our other examples, I'll stick with apples here. Unless both have the same class concept of what an apple is, then applying the Law of Non-Contradictories is meaningless. For the term "apple" to have meaning and relevance, both the author of the proposition and the one to whom the proposition is communicated must have agreement about what consitutes the class concept of "apple-ness." The more agreement within the class concept, the more "meaningfullness" being communicated.

If both the author of the proposition and the one to whom it is communicated do not have a significant alignment on Identify, then applying the Law of Non-Contraditories is of no value in determining the "truth" or "error" of the proposition and neither is the application of the Law of Excluded Middle.

I have removed this, which I don't understand, from the formal logic section.


 * In the calculus of classes, disjunction elimination and conjunction elimination are also invalid, for, from the statement that the class $$a \cap b$$ is null, we can't conclude that one of the classes a and b is null; and from the statement that the sum $$a \cup b$$ is equal to the whole we cannot conclude that either is equal to the whole. But these implications are true in propositional logic.

I don't see that it is consistent with the linked definitions, for one thing.

Charles Matthews 11:15, 28 Jan 2004 (UTC)

The proof of non-contradiction in the Aristotelian Logic section contains the premise "it is only the law of non-contradiction that prevents " can be" from necessarily becoming "is"). ". This needs to be elaborated upon.  "can be" has no translation in propositional logic as far as I know.

As someone who studied mathematics at the university level, I think the statement copied below, and the "proofs" that follow do not prove that the laws of non-contradiction and the excluded middle aren't axioms in a formal mathematical system:


 * Some have considered classical logic to be just like a mathematical theory, and in particular the laws of non-contradiction and the excluded middle to be simply axioms of the theory, which have to be assumed without proof. In fact this is not so...

The reasoning in the "proofs" which follow that statement belong to something that I would characterize as meta-mathematics. That is the "proofs" implicity assume that you know what is meant by the atoms "true" and "false". But if you consider Aristotelian logic as a mathematical system then the atoms are only defined by their use in the two axioms. In a mathematical system there is no way to define such basic terms as "true" and "false" without the use of axioms.

Since the "proofs" given are interesting on philisophical level, I don't think erasing them would be warrented, but I was wondering if anyone had any ideas on how to make it clear that the "proofs" given don't satisfy actual mathematical rigor. millerc 21:14, 19 Mar 2004 (UTC)

Compuetr logic
User:152.163.252.131 added:


 * The basic definition for computer LOGIC is that it is the sequence of operations performed by hardware or software.

There is perhaps something useful to be said about computer logic (e.g. TTL), but this is simply confusing (and non-wikified) as a first paragraph. Bovlb 12:35, 2004 Apr 28 (UTC)

I'm just a curious beginner who found the logic article interesting, but would someone be kind enough to say whether Bill is a 'knight' or a 'knave' in example 3:

>Logician: Are you both knights? John: Yes or No. Logician: Are you both >knaves? John: Yes or No.

>Who is who?

I tried using the notation given for example 1, and went from



(J \wedge ((J \wedge B) \vee (J \wedge B)') \wedge ((J' \wedge B') \vee (J' \wedge B')')) \vee (J' \wedge ((J \wedge B) \vee (J \wedge B)') \wedge ((J' \wedge B') \vee (J' \wedge B')')') = \mbox{tautology} $$

to



J = \mbox{tautology} $$

which seemed sensible as John is obviously a knight and there doesn't seem to be any information about Bill? ..Help :)

I suppose a point I'm trying to raise, is how beginner friendly should the wiki be. Should any rational thinking newbie be able to understand any given topic in the wiki by following enough links? ..or would this make the wiki too verbose?

Page Goals and design
This article needs more careful editing.


 * For instance, predicate logic is a kind of formal logic (as well as propositional logic, temporal logic, Hoare logic, the calculus of constructions etc.) this isn't clear from the article and some at least cursory mention of this fact should be made.


 * The distinction between formal logic and mathematical logic needs clarification. Is it because it mathematics applied to logic (which I think is the answer) and in particular can include model theory and proof theory.


 * Aristotelian logic is important historically, and I am reasonably happy with essentially a link to the article of the same name which is informative. That probably could stay as it currently stands.

CSTAR 00:25, 5 Jun 2004 (UTC)


 * Yeah, this article has some good info but definately needs more editing. I think that the page itself should not be overly technical, which is the path it has taken recently.  Besides serving as a definition and glorified disambiguation page, it should definately give a good background of logic, probably even its history.
 * Devote the page "Logic" itself to a few things.
 * What logic is, definition (this should obviously be on the page)
 * The general, various goals of logic (to explain to people why it exists)
 * The recently made informal vs. formal clarification.(Could be part of the definitions section)
 * The current links to the various types of logic with short descriptions (Helps to disambiguate clearly)
 * The background of logic, and history
 * I think the History of logic section should be the real heart of the article, actually. It'll keep the article interesting to those browsing, and people just looking for a general idea of logic, and it'll also be a nice central place for information about logic in general.  It also won't get in the way of people that were looking for somethign more technical, because they'll find one of the disambiguation links first. The history section will also be excellent to help allow this page to link to the important people and results of logic, Aristotle, Descartes, Frege, Godel, Turing, etc...
 * In general, This page should be the defining Wikipedia page on logic, and basically be able to take you wherever you want to go, while providing lots of interesting information on the subject
 * siroxo 23:56, Jun 10, 2004 (UTC)


 * I recently removed the History part out becuase the information did not fit well with what was there. I'm not sure I understand what you mean by the background of logic is. I think the reason to keep the history section out, other than a list of bulleted items and links, is that Historical questions and debates can be very difficult. This way we can safely relegate that debate to  a different page. One thing I disliked with the previous versions of  this article was the presence of too many topics, some redundant and some far too wordy.


 * We also need to decide on some philosophical issues: An important distinction is between deductive and inductive logic. This article I believe should be mainly deductive logic. Inductive logic is more complex.  This is different in my view from the distinction between empirical knowledge and a-priori knowledge. I'm perfectly happy to entertain the idea that logic is emprirical but discussions of this kind should not be a part of this article.


 * CSTAR 01:22, 11 Jun 2004 (UTC)


 * Yeah, i saw that you took the history out, and that is certianly fine with me, since it didn't fit well. I'd advocate developing the history page more, in parallel with this page, and then perhaps reuniting them if it seems like a good idea.
 * I guess my main priority is to make sure this page remains useful beyond just a disambiguation and clarification page. It should be useful as those, but should provide some more interesting content about what logic is, how it relates to other subjects (esp. philosophy), and how it developed over time.  Technical pieces should not be included, those should be relegated to whatever sub-topic they belong to, as they are for the most part.  Logic is a broad topic, so this should not try to hard to explain any one piece of it, but should try hard to put these pieces together, and then link to them.
 * siroxo 03:58, Jun 11, 2004 (UTC)

- I've created a possible outline for the logic page, I believe it can provide an excellent general idea of what logic is, with enough specifics to distinguish topics for the reader, and lead him/her to appropriate topics. I also belive it provides a broad enough description of logic that it has the nature of an encyclopedia article. Please critique and make suggestions!

siroxo 15:03, Jun 12, 2004 (UTC)
 * 1) Intro (Above TOC)
 * 2) *Defintions
 * 3) **"Laymans" general definition (marked as a non-technical def)
 * 4) **A more techinical definition
 * 5) *General Study of logic (background stuff about relation to Philosophy, Math, Computer Science, etc) more detailed explanations follow, and exist in other articles.
 * 6) Clarifications
 * 7) *Formal vs. Informal logic
 * 8) *Deductive versus Inductive reasoning
 * 9) A short background of the history of logic with links into the history of logic as necessary, hopefully relating the following "logics"
 * 10) Types of logic (each has link to "Main article, as currently, with a short description)
 * 11) *Formalisms
 * 12) *#Propositional/Sentential
 * 13) *#Predicate/First Order
 * 14) *#Higher Order
 * 15) *#Mathematical
 * 16) *#Modal
 * 17) *Less formal (and informal) systems and topics (Many of these contain formal elements, but are not formalisms themselves)
 * 18) *#Aristotelian logic
 * 19) *#Philosophical logic
 * 20) *#Logic and Computation
 * 21) *#Multi Valued logic
 * 22) *#Logic and Computation
 * 23) See also (incorporate as many of these into above text as possible)

I am in general agreement with the outline. However, my most cherished principle of writing is this:
 * Lo bueno si breve, dos veces bueno,

which I learned in my Spanish Jesuit high school, meaning The good if brief twice good. This principle is particularly important in an article on logic!

CSTAR 16:35, 12 Jun 2004 (UTC)

I've seen the page in a number of versions - none of them really good. I really think it suffers every time it gets closer to the kind of computer science thinking (roughly speaking, you can have any kind of formal system you want and call it the XYZ logic, if you think you have an application).

I'm not an expert, but the history tells one something. There was an old meaning of formal or symbolic logic (already in Kant?). In the nineteenth century logic was formalised first for pedagogic reasons (Boole, Lewis Carroll) - because it was still considered a pedagogic subject. Only with Frege did it really become once more a research area (after 2000 years). I don't believe there really was a subject called mathematical logic, before Gödel. The need to write what he had done in a way that could be understood made for recursion theory first, and then model theory, as disciplines within mathematics. So basically one can say that the incompleteness theorem directly caused those developments. For example, for the Polish school at its foundation, logic was not 'inside' mathematics at all; but a separate subject. And before that the philosophers were sorting out philosophical logic, i.e. parts of the logic of natural language that are difficult to formalise.

After 1950 it really is all less clear ...

Charles Matthews 18:50, 12 Jun 2004 (UTC)

Well I agree that specialized formal logics, particularly for reasoning about a specialized subjects such as concurrency or computer programs really should have a subordinate position in the article. I was trying to achieve that goal--- for this reason I introduced the section header highlighting the distinction between formal and informal logic. Apparently I didn't quite achieve that yet.

However, I would stress the following points:


 * Though history of logic is exceedingly important, it is also very specialized so that that this subject should be clearly delineated and preferably discussed somewhere else.


 * The logic page should have a practical purpose, for someone trying to distinguish between good and bad argument. In this regard the article on logical fallacy is extremely important. See the paragraph in the intro to David H. Fischer's book Historians Fallacies dealing with the argument that emphasizing fallacies in logic is explaining how to get from Boston to New York by describing the roads that don't go there. His response: It is useful to know places where one might get lost in this trajetory. (Having done this trip many times, this is very good advice to have, particular near NY)


 * The concept of a valid inference is important. This article currently stresses deductive validity as opposed to inductive validity.  This is OK, in my view since induction is much more complicated and uses deductive validity


 * Mathematical logic as we currently understand it (as is correctly formulated in the article mathematical logic: application of mathematics to logic and inference) probably does originate with Godel. However, Peano, Poincare, Hilbert, Russell and Whitehead did refer to something called mathematical logic which today we might think of as sterile formalizations of mathematics. Symbolic logic is a term which is probably even older.

I noticed that the Routledge Encyclopedia of Philosophy does not have an entry on Logic pure and simple. It has lots of entries logic of XYZ.

CSTAR 20:26, 12 Jun 2004 (UTC)

Plan of action for the logic page
Is there one? CSTAR 16:14, 20 Jun 2004 (UTC)
 * I was busy the last couple weeks, but I have time to work on this page again. I suggest we start working on setting up a good introductory definition and make the clarifications very clear, then attack the rest of the page &mdash;siro&chi;o 03:31, Jun 24, 2004 (UTC)
 * One of the things which is not clear from the introduction currently is the difference between inference and argument. Argument I guess is the linguistic or symbolic expression of inference. One can infer something (in one's head)  without an argument.CSTAR 04:12, 24 Jun 2004 (UTC)

I suggest: traditional logic discussed in general terms, up to the time of Boole and Mill (on induction) when things started to shift. Then mathematical logic Frege up to about 1940 (when the structure of the subject had become reasonably clear). Philosophical logic had a definite meaning for Russell, which then moved somewhat; but this is still a key area for analytic philosophers.

Charles Matthews 07:21, 24 Jun 2004 (UTC)

- I just reworked the intro a bit. Tried to make it flow better, as well as adding an idea or two. One note, I think the first sentance, as it is in the new version, is required. In common conversation, logic basically just refers to the reasoning used to reach a conclusion. I think we should allude to that, and then introduce the formal concept. This will even help to reinforce the formal view of logic to people who have not studied it, as well as easing people into the article.

I also resectionized the first couple sections, and dropped the deductive/inductive thing into there, I hope it fits better like that.

Regarding inference/argument, I'm not sure how to convey that in this page, but it might be an interesting addition.

&mdash;siro&chi;o 09:08, Jun 24, 2004 (UTC)

I made some small changes to the first paragraph.


 * Replaced at its most basic with ordinary language. I think that's what we mean; although go ahead and revert if you disagree. I'm not trying to be ideological. I have a nasty habit of pondering every word, which means I never get very far.


 * I used inference instead of argument-- argument implies communication. I've spent some time working on the article logical argument where that distinction is made.


 * Corrected two typos (assumption was mispelled)

CSTAR 14:27, 24 Jun 2004 (UTC)
 * Good points all around, i like the ordinary language especially &mdash;siro&chi;o 19:54, Jun 24, 2004 (UTC)

The most recent edit (Lorenzo Martelli) tries to clarify the situation in which the assumptions are inconsistent --- is this really necessary? If they are inconsistent, the premises will never hold and by the meaning of material impication, validity is vacuously true. Mainly I don't think this should be put into the introduction, maybe some other place. Otherwise the introduction is very rapidly going to get unwiedly. CSTAR 15:36, 24 Jun 2004 (UTC)

Reply from Lorenzo: I agree in general with your comments CSTAR. Maybe then we should just leave in the qualification 'for most intents and purposes'? What I think would be wrong would be to have a statement beginning 'Validity means .....' in the introduction to an article on Logic, if that statement is not 100% accurate. After all, half of the reason behind formal logic was to get rid of the ambiguities...!I also think we should put somewhere in the article a strict definition of validity, of the form 'an argument is valid if and only if...' to ensure it is clear and referenceable, and that all that follows (the paradox of entailment etc, why truth tables are so important)can be explained through/referred back to the definition. Hope you agree and if so feel free to move my comments to a more appropriate place.


 * Validity is important enough to define on the page without going into the detail of the validity article. Where it is right now seems quite appropriate, as a reader interested mainly in validiity will click the link in the intro, and a reader interested in logic will still get a chance to see basically what it means.  Now we shoudl figure out how to approach all these types of logic.  I like having small introductions with "Main article" links.  It helps to give a deeper background of what logic is, and to disambiguate, but we need to organize them appropriately and give them a good introduction explaingin why they are divided such  &mdash;siro&chi;o 19:54, Jun 24, 2004 (UTC)
 * I think one way one can argue that logic is an empirical science is that various notions of validity are models of an ideal notion of validity. This isn't too hard to argue for inductive validity and definiong deductive validity in some semantic way is also an approximation.  I agree these should be placed in the article, but not in paragraph 1.CSTAR 20:09, 24 Jun 2004 (UTC)

Specialized logics
Could we collapse the sections on Multi-valued logic and Logic in Computer science into a single section, say specialized logics. Also I prefer to use inference instead of reasoning in the section currently titled deductive and inductive reasoning. For example. inference could be procedural, i.e., apply Matlab to infer something. I think also a sentence or two on the distinction (and also relations) between inference and logical argument is necessary. CSTAR 16:07, 1 Jul 2004 (UTC)
 * I made minor expansions to multi-valued logic, but I believe that since several major concepts in logic, and related concepts are founded in multi-valued logic, it should have its own section. I divided otu the CS/AI section from what I now call "Types of logic" (needs a better name), and I think it sits well as a separate idea.  Also, IMHO, you should feel free to make any changes regarding inference/reasoning/logical argument.  If they are confusing, just make an explanation.  The page will evolve to incorporate them even better, as well.  &mdash;siro&chi;o 11:40, Jul 5, 2004 (UTC)

Possible revision of first paragraph
I know we have beat this subject to death, but I am still unhappy with some of our characterizations of logic given in the 1st paragraph, particularly, since in the broad sense that logic traditionally has had in philosophy, it is concerned with the structure of inference. Thus I propose a change starting at the second sentence:


 * More formally, logic is concerned with inference, that is, the process whereby new assertions are produced from already established ones. Of particular concern in logic is first, the structure of inference, that is the formal relations between the  the newly produced assertions and the previously established ones (formal, in the sense of being independent of the assertions themselves) and second the investigation of validity of inference, including various possible definitions of validity and practical conditions for its determination.  It is thus seen that logic plays an important role in epistemology, that is it provides a mechanism for extension of knowledge.

CSTAR 04:33, 31 Jul 2004 (UTC)


 * Excellent, worth beating to death if it can be clarified better ( Yours is much clearer about the general idea of formal logic. I've repasted it here, with a couple grammatical changes I suggest for clarity.
 * More formally, logic is concerned with inference&mdash;the process whereby new assertions are produced from already established ones. As such, of particular concern in logic is the structure of inference&mdash;the formal relations between the the newly produced assertions and the previously established ones. Where formal relations are independent of the assertions themselves. Just as important is the investigation of validity of inference, including various possible definitions of validity and practical conditions for its determination.  It is thus seen that logic plays an important role in epistemology in that it provides a mechanism for extension of knowledge.
 * &mdash; siro &chi;  o  10:28, Jul 31, 2004 (UTC)

Dialectic and rhetoric
I'm not sure I agree with the opposition of rhetoric (and dialectic) to logic. The relation between the is complex, that's clear, but to say it is one opposition is also misleading.CSTAR 14:11, 12 Aug 2004 (UTC)


 * Quite so, and a brief discussion of the Organon should make this clear Charles Stewart 15:44, 14 Aug 2004 (UTC)

Missing core topics

 * Central tools of logicians: proof theory, model theory, and possibly more sophistcatedly mathematical tools such as set theory, recursion theory and category theory.
 * Controversies in logic: eg. intuitionism, relevantism.
 * The scope of logic: non-deductive inference forms, eg. induction and abduction (shouldn't say too much here, hive off on an AI or knowledge representation page).
 * Modern research innovations: substructural logics, hybrid logics, non-commutative logics.
 * Quantification: relate to problem of multiple generality in Aristotelian logic.

Any problem with me charging ahead and adding these? --- Chalst 23:55, 11 Aug 2004 (UTC)

-
 * Keep in mind there are (or at least should be) specialized articles on all of these. There are certainly articles on quantification, model theory, proof theory, set theory, recursion theory the subjects you mention. I suggest you poke around first.  ALso this logic article took a long time to stabilized to its current form.  CSTAR 00:12, 12 Aug 2004 (UTC)


 * Most have topics, some do not. I think all of these are floating near enough th e top that a good overview should at least point to the topics in an informative way.  Also, I think a weakness of the article as it stands is that the place of logic is not as clearly defined as it should be (the Organon took a central place in Aristotelianism), and also some mention should be made of in virtue of what do logicians think logic to be true.  I think I can avoid vandalising the page. nCharles Stewart 01:20, 12 Aug 2004 (UTC)


 * Well good luck! CSTAR 04:20, 12 Aug 2004 (UTC)

Intuitionism and relevantism probably deserve a mention. I'm not too familiar with the modern research you allude to. Everything else i'm not sure yet, might as well add some stuff and we'll see where it goes. Just remember that this is not the main article on any of those topics. &mdash; siro &chi;  o  01:13, Aug 12, 2004 (UTC)

-

I've created two short articles semantics of logic and proof-theoretic semantics (among others) prior to editing the Logic page proper. Close readers may notice that there are some disagreements of fact between those articles and this one. Comments welcome. Charles Stewart 23:35, 18 Aug 2004 (UTC)


 * Although my own preference is not to regard proof-theoretic semantics as semantics, you are right to include them both. However, I think it would be far too narrow to exclude informal logic within the broadest scope of logic. I for one am not sure where to draw the line between logic and non-logic; For this reason I prefer to think of logic as the structure of inference and as a particular case the structure of argument.  For instance Structure of argumentative dialogue  can be (and recently has been) formalized as a communication protocol where messages sent or received by a protocol participant depend on current commitments and pending challenges.  Also structure of argument is important in just about any field of endeavor -- economics and political science come to mind.  The play between formal models and informal reasoning is intriguing.


 * None of this is intended to dissuade you from including those articles in the logic page. They are well-written, but I don't think it would be accurate to entirely supplant logic with this formalized idealization.CSTAR 02:30, 19 Aug 2004 (UTC)


 * Thanks for the comments. These other pages are meant to stand on their own, they are really stubs and need much more development, and I plan on putting shorter summaries of the topics on the main logic page.  Regarding informal logic: I am a partisan on this issue -- the opening sentence of my doctoral thesis runs "Logic is the study of arguments correct in virtue of their form", and the first footnote says, in effect, that the term informal logic is perhaps a misnomer -- it is the study of arguments whose form is concealed in the deep structure of language.  Charles Stewart 09:43, 19 Aug 2004 (UTC)


 * That view of informal logic is fine by me; I just try to be careful not to fall into naive reductionism --- that natural language reasoning is either meaningless or reducible to reasoning in a formal sequent calculus (I tend to fall into this, being a mathematician ). Maybe you should have at the logic page, and while your at it, also the logical argument page. I also started a political argument page which is in need of serious attention. CSTAR 21:30, 19 Aug 2004 (UTC)

Types of Logic
I don't like the current organisation of this section. It's possible to organise logic by its formal type, when one gets a list along the lines of:
 * Syllogistic
 * Stoic (propositional)
 * Boolean
 * Predicate
 * Other

Or one can organise it by motivation/application, and get:
 * Philosophical
 * Dialectical (Aristotle's motivation for the Organon was as a tool for reasoning and argument)
 * Mathematical
 * Computational

Mixing the two axes, as is done now, though, seems like a recipe for confusion. The first list seems more important to me.

Furthermore, "Multi-valued logic" as a category of logic, is just wrong. It's an issue in the semantics of logic: one can give multi-valued semantics to FOL, and there are non-bivalent logics, such as intuitionistic logic, that are not commonly treated as being truth-valued at all. The existence of multi-valued logics is maybe appropriate in a semantics section, or in the section I proposed earlier on controversies in logic.

If there are no objections, I'm planning on applying a series of changes in the next few days, starting from tomorrow evening Charles Stewart 14:31, 17 Aug 2004 (UTC)


 * I agree that Multi-valued logic as a category is wrong, although the preferability of one "axis" to another is not clear to me - yet; I also think that the distinction currently made between "informal logic" and "formal logics" at the beginning of the article is useful.CSTAR 14:44, 17 Aug 2004 (UTC)


 * Since some of the changes I am thinking of applying will be controversial, would it be a good idea to make a mock-up in a page called, say, Sandbox/logic? Charles Stewart 16:14, 17 Aug 2004 (UTC)


 * I suppose it doesn't really matter, since one can always revert. CSTAR 21:09, 17 Aug 2004 (UTC)

Big changes applied
Now applied the restructring I've been threatening... Two issues:

''Aristotelian logic is sometimes referred to as formal logic because it specifically deals with forms of reasoning, but is not formal in the sense we use it here or as is common in current usage. It can be considered as a precursor to formal logic.''
 * I've deleted this, because I think it is wrong: it is perfectly easy to see how syllogistic is formal, c.f. the work of John Corcoran expressing syllogistic in modern notation. Do any authorities seriously dispute the formal nature of syllogistic?  I would be surprised.  I've completely rewritten these paragraphs.

Mathematical logic refers to two distinct areas of research: The first, primarily of historical interest, is the use of formal logic to study mathematical reasoning
 * Not at all! The application of logic to the study of mathematics and mathematical proofs is still one of the main driving forces of mathemcatical logic.  Just look at applied model theory, reverse mathematics, Borel spaces.  I've completely rewritten this paragraph.


 * I obect! I wrote that sentence! By that I meant the following: once it became clear (in historical time possibly in the late 1920s but I'm guessing) that informal arguments in mathematics can be reduced to purely formal proofs, hardly anyone regarded purely formal proofs as useful (caveat of course: formal verification does stress formal proof and it is useful, I suppose for many critical applications, but it is highly debatable whether formal proof-checking is mathematics at all! Despite MIZAR and Isabelle, in the current state of the mathematical sciences it would be misleading, I think, to regard this area  is of any interest outside of a relatively small group of specialists.  This of course is a sociological fact more than anything else, but in fact the assertion in question is also sociological).  Notice that I stated
 * use of formal logic to study mathematical reasoning


 * The area of research you describe in Borel spaces or model theory (which I think would include non-standard analysis) could be called formal logic only by a stretch, I think. In other words, though logic may occur in the subject of these investigations, logic is itself regarded as an object of study (e.g., somewhat fancifully, say one could regard formal structures as a kind of space on which a group acts such as a Tits building or some such thing -- and actually as you point out above somewhere domain theory is an area where the mathematization of formal systems becomes more visible ). CSTAR 02:55, 26 Aug 2004 (UTC)


 * I guess it's possible to argue that both what I changed this section from and what I changed it to are not NPOVs. I hope not, because I like what I wrote.  OK, quibbles with what you wrote first: all the stuff about Borel sets, analytic sets, projective sets did change the systems that set theorists studied, since they gave rise to new large cardinal axioms via the work on descriptive set theory.  By applied model theory, I mean the stuff that MacIntyre was doing -- applying model theoretic techniques to algebra to get new mathematical results algebraists think are valuable; it really couldn't be a clearer application of logic to mathematics; whilst in reverse mathematics, you need to really go back and think about how you prove things one is really recreating mathematics according to logically imposed constraints.  With Macintyre's work, I think it couldn't be clearer that the objectives are mathematical ones (indeed, see  why this might not be logic anymore...), and withthe other two, while we may have foundational motivations for studying them, it should be clear that the objects of study themselves are mathematical.  I think from this point of view, what I wrote is OK (do I need to say more so that this is clear?)


 * There is another issue you raise, namely that few logicians (the applied model theorists being exceptions) are genuinely close to mathematical practice. In fact I'm reading a nice book by David Corfield at the moment "Towards a Philosophy of Real Mathematics", and it is abundantly clear that he would agree with you.  When a logician studies mathematics, he learns something, but not something that is of much use to the mathematician, and this is something that the pioneers of mathematical logic did not expect.


 * Resolution: maybe we need to divide up mathematical logic into more kinds of activity: both foundations of mathematics and applied logic would fall under the use of formal logic to study mathematical reasoning, and maybe we need to make clear that these are two different kinds of activity. Charles Stewart 10:01, 26 Aug 2004 (UTC)


 * Do I have the right indentation here?... :)


 * Yes I generally I am very happy with what you wrote -- though I think the point I raise is more than a minor quibble. In applying logic (i.e. model theory) to mathematics in the way you mention is hardly different than noting that the transfer principle is useful in translating certain nonstandard statements to standard ones. I use this equivalence just because I am very familiar with non-standard analysis. Now where does logic begin or end in non-standard analysis? This is the perennial question, what are the limits of pure logic? I certainly don't know.


 * But my main point is that the study of logic and logical systems is more like the emprirical study of physics: There are these systems of inference, we propose models for them and study them using mathematics. I believe a very weak version of this in that I am not a Putnamist on this, i.e., I am not prepared to argue as does Putnam that logic is empirical. See Quantum logic.


 * BTW the logic page as it now stands is of very high quality.CSTAR 13:49, 26 Aug 2004 (UTC)

Comments welcome on all changes Charles Stewart 00:36, 26 Aug 2004 (UTC)


 * I merged the "types of logic" and "motivations for logic" sections, because it was confusing to have types split between the two. The specific motivations are inherent to what type of logic being considered, though so I think they go well together this way.  Perhaps a little general idea of motivation could be placed in the introductory secont above the TOC if you wish. &mdash;[[User:Siroxo| siro  &chi;  o

&mdash;siro&chi;o]] 05:03, Aug 26, 2004 (UTC)


 * Hmmm. I separated them out because it was clear to me that they were different kinds of subsection: in particular, I don't think that, say, mathematical logic is a type of logic, but rather a set of interests and concerns that certain kinds of logician bring to whatever branch of logic they study.  Philosophical logicians and mathematical logicians study one and the same first-order logic, and they study one and the same S4 modal logical system.  Instead, they just ask different questions about them, and do different kinds of investigations into them.  I agree, though, that "motivations for logic" was a clumsy section heading.  Maybe "Types of logician" would be better...


 * On rereading what I wrote, the preamble to the types of logic section is not consistent with the contents, and so needs to be rewritten anyway.


 * And thanks for the cleanup work with the all the red I left on the pages, and sorry there was so much: I actually 'corrected' many of these links, but corrected them to new broken links. Charles Stewart 06:32, 26 Aug 2004 (UTC)


 * You make a good point regarding "types" of logic and all. I changed the name to "paradigms of logic" in hopes that it would imply a more general idea that these were various ideas that different logicians followed. &mdash;[[User:Siroxo| siro  &chi;  o

&mdash;siro&chi;o]] 07:48, Aug 26, 2004 (UTC)

Mathematical logic
The article currently states:


 * Both the statement of Hilbert's Program and it's refutation by Gödel depended upon their work establishing the second area of mathematical logic, the application of mathematics to logic in the form of proof theory.

Is model theory usually considered part of proof theory?


 * No, but in context, Hilbert's program centred on the role of consistency statements, which are considered a part of proof theory. Goedel's completeness theorem states a key result in model theory, but the machinery he used to prove it is proof-theoretic (the original theorem used esentially a proof search algorithm).

If so that's news to me. Model theory certainly is mathematics applied to logic.


 * If proof theory and model theory have been the foundation of mathematical logic, they have been but two of the four pillars of the subject. Set theory originated in the study of the infinite by Cantor, and it has been the source of many of the most challenging and important issues in mathematical logic, from Cantor's theorem, through the status of the Axiom of Choice and the question of the independence of the continuum hypothesis, to the modern debate on large cardinal axioms.

These seem like fairly subjective evaluations. Are we sure it's four pillars and say not...sixty five pillars? (I'm being a little facetious here purposely to spice up the discussion). I concede that these boundaries are really murky, but is set theory really logic?


 * Indeed, it is subjective, so maybe a remark to that end is in order. But it's a pretty standard way of dividing up the field since Barwise's 1977 Handbook of Math. logic.


 * Ok that is an important fact and probably should be stated here (or in some referenced article).CSTAR 15:33, 29 Aug 2004 (UTC)

And I think we should be less harsh on the logicist programme. Saying it was a failure really gives an erroneous impression. The logicist program did succeed in one way: As a result of the logicist programme it became abundantly clear that mathematical reasoning is in principle reducible to a formal calculus (if anybody has enough time or funding on their hands to do it)


 * It failed according to its own criteria, but as I said, there was a silver lining Charles Stewart 15:02, 29 Aug 2004 (UTC)


 * P.S. Actually as I said earlier I like very much what you added, it's just that I'm not sure the limits of mathematics and logic are adequately discussed (and I don't claim to know the answer either)CSTAR 04:52, 28 Aug 2004 (UTC)

Dialectics and rhetoric
I think the article still gives short-shrift to Dialectic and rhetoric. It ignores the work of Chaim Perelman and Tyteca-Olbrechts on argument. This is briefly mentioned in logical argument.


 * I've put a comment on the talk page of that article. There is a section, so far with no body, that I created, entitled dialectical logic, which seems the natural home for the work of Perelman & Tyteca-Olbrechts as you have described them.  Charles Stewart 13:07, 30 Aug 2004 (UTC)

Logic is not the study of reasoning
Or rather, to claim it is, is to take a psychologistic view of logic, one that is almost universally rejected by modern logicians, although one that was popular in the last half of the 19th century. The psychology of cognition is the study of reason. &mdash; Charles Stewart (talk) 08:52, 11 February 2010 (UTC)
 * Do you have a proposal for alternative text? I think your objection is valid when you're looking up close in detail, but on the other hand "the study of reasoning" is a reasonable description of the broad motivations of logic.  It has the ring of a traditional definition (like the one at mathematics about "time, space, structure, quantity, change" or whatever it says now).  I would kind of expect "study of reasoning" to be at least mentioned, though I agree that it's problematic to present it as comprising logic as a whole. --Trovatore (talk) 22:14, 11 February 2010 (UTC)
 * How about what we had before, the last time I complained about the poor lede and fixed it? I've really no interest in applying edits to the logic articles that will just get changed by people who have their own ideas, and aren't willing to see that they are just personal opinions.  I am not willing to take any responsibility for the contents of this article anymore.  I'll just drop by a couple of times a year and maybe complain nonconstructively.
 * The problem with "study of reasoning" is two fold: plenty of reasoning is subject specific "I hear the kettle whistling and so I infer the water for my tea is boiling", and second, most logicians don't consider the pragmatics of how logical inference is actually carried out to be within the scope of logic, but rather part of epsitemology or psychology. This, it is true, is a change from how things were a century or so ago, but that's how it is now.  &mdash; Charles Stewart (talk) 10:00, 12 February 2010 (UTC)
 * I understand what the first poster means. For instance, to be connected to someone "biologically", you do not mean that you are connected to them in a "manner of thinking" (specifically in a manner of thinking about evolutive processes), but you are connected in an actual sense (you are connected to them evolutively regardless of whether or not you are thinking about it).  So "logic" must have some more fundamental meaning than just "the study of reason", that would be something named "logicology", but Logic itself lacks a proper examination in this article.  —Preceding unsigned comment added by 24.136.33.194 (talk) 01:07, 24 February 2011 (UTC)

Misuse of sources
is one of the main contributors to Wikipedia (over 67,000 edits; he's ranked 198 in the number of edits), and most of his edits have to do with Islamic science, technology and philosophy. This editor has persistently misused sources here over several years. This editor's contributions are always well provided with citations, but examination of these sources often reveals either a blatant misrepresentation of those sources or a selective interpretation, going beyond any reasonable interpretation of the authors' intent. Please see: Requests for comment/Jagged 85. That's an old and archived RfC. The point is still valid though, and his contribs need to be doublechecked. I searched the page history, and found 18 edits by Jagged 85 (for example, see this edits). Tobby72 (talk) 16:59, 12 June 2010 (UTC)

2nd nonconstructive complaint
I see that the article has a new, up-to-date reference for "Logic is the study of arguments", from the 2002 book by the Catholic philosopher, Harry Gensler, of the John Carroll University, a Jesuit theological college.

Modern Catholic teaching of logic has perhaps been unduly neglected in Wikiedpia's treatment of logic, but it is certainly not mainstream. What, precisely, is wrong with the definition in the Collins Encyclopedia, which was edited by the highly accomplished scholar, David Crystal? What is the attraction of this offbeat definition of logic, that we have to spend so much effort furnishing it with references? Is Harry Gensler really being held up as such a great authority that can tell us that Tarski's characterisation of logic as concerning non-subject specific consequence has been overturned?

Perhaps this article will attract attention from a competent editor who can see beyond their personal views on what logic is, and see how experts use the term. Until then, look out for my 3rd nonconstructive complaint. &mdash; Charles Stewart (talk) 10:12, 26 October 2010 (UTC)

Logic-the tool.
I propose that the description of Logic should be fundamentally altered. To say that logic is 'the tool for distinguishing between the true and the falce' is to say that there is an observer who uses 'the tool' to judge what is true and what is falce. This does not say what that 'tool' is. That which is observed in the observers consciousness in the 'now' is a static picture. Using logic the observer, under the influence of motivation, alters that picture for another picture in the next 'now'. The change occurs in time. Both pictures are static at the time of observation. What is it that directed the alteration of the first picture to the second picture ? The observed picture in the first 'now' consists of parts. Each part is an independent truth defining the whole of the picture. The same applies to the picture in the second 'now', after change. Some of the truths of the description are common for pictures in both observations. The more of the truths of the description are common the stronger is the logical connection. Logic is like magnet. It has variable strength depending on how many truths about the two interacting pictures are common. KK (78.146.68.198 (talk) 13:24, 13 March 2011 (UTC))

Disambiguation talk
I think some of the comments have been moved I found an old contribution in the talk page of the disambiguation, but I amsure it was originally written on the main article. Can someone please explain, in their own words, the history of the article and what happened? Kathybramley (talk) 06:23, 27 March 2011 (UTC) This is my text from the disambiguation talk page: What about logic in the more everyday use in speech? When someone, like a doctor, suggests you are not as logical as you think, what do they mean? What exactly? How can you challenge or assess that? I'm not sure the mere mention of cognitive psychology really covers it, not from a user-friendly way. I imagine people using this page to get ideas if the word 'logic' has come up as an accusation of lacking it. What about logic and logical structure in essay writing/general academic writing? (I was always getting comments 'could be more logically structured' through school up to degree, but never once did anyone describe 'logical'). It is in this case, logical structure is equating to outline structure - starting with a distilled strong central/over-arching idea and 'exploding' it into constituent parts in a step-by-step fashion. I want a link from this page to an appropriate page. I'd like it for both these instances of important areas of use that are not yet included. ...not sure I am brave enough to yet though (quite a new user I am). Ideas and help? Comments? Kathybramley (talk) 19:06, 19 April 2009 (UTC) Kathybramley (talk) 06:23, 27 March 2011 (UTC)

Induction as Logic?
I think that in general, inductive reasoning is not considered logic; that is purely restricted to deductive reasoning. Inductive reasoning commits the inductive fallacy and is illogical. To give an example of inductive reasoning and why it is flawed, consider the following example: a hen who is fed and taken care of by a farmer day after day. The hen could inductively conclude, that the farmer will continue to do so based on this observation, corresponding to a premise in deductive reasoning. However, one day the hen is butchered by the farmer and fed to the family. Clearly the conclusion the hen came to was flawed -- it assumed constancy in the universe. This is the flaw of induction and why it should not be compared so closely with deduction. This article should be edited to express that. MONODA (talk) 10:19, 3 May 2011 (UTC) Dear MONODA...your hen pretended to know the future. Logic deals with the relationship between two static pictures in the 'now'. KK (78.146.69.242 (talk) 22:27, 3 February 2012 (UTC))


 * Inductive logic is a branch of logic. It generally deals in evaluating uncertainties and probabilities, and historically gave rise to modern probability theory. Tashadox (talk)

Expand discussion of China and India?
There's plenty to do! Here are some resources to start:

Dan Cottrell (talk) 00:12, 19 June 2012 (UTC)
 * http://plato.stanford.edu/entries/early-modern-india/
 * http://plato.stanford.edu/entries/school-names/
 * http://plato.stanford.edu/entries/mohist-canons/
 * http://plato.stanford.edu/entries/logic-india/
 * http://plato.stanford.edu/entries/logic-paraconsistent/

"Logic garnet"
A new user has added an intriguing picture of a so-called "logic garnet", claiming that it's an "early device used to determine the logical consistency of a given claim". We don't have any article directly on this, but we do have one on Shea Zellweger, who seems to be the inventor. Zellweger was born in 1925, so the thing can't be that "early" really.

I don't mind the picture, and a mention, somewhere in the article, but I'm not sure that an idiosyncratic notation deserves to be placed so prominently at the top. There are lots of notational systems that have accumulated followings of devoted fans but never really caught on in the wider world (e.g. Sheffer stroke, Laws of Form). --Trovatore (talk) 20:11, 3 September 2011 (UTC)

MAJOR problem with this article
The first two sentences of this article are self-contradictory.

"Logic is the study of valid reasoning. Logic is used in most intellectual activities."

This is entirely wrong. The study of valid reasoning is most definitely NOT used in most intellectual activities.

Are you people okay with me changing it in a major way?

Another contradiction, still in the opening paragraph, is mention of "The study of logic". Since "logic" has been defined in the first sentence as "The study of valid reasoning" then "the study of logic" would be the study of the study of valid reasoning. This is ridiculous. Am I the only person who can see this?

— Preceding unsigned comment added by Ksolway (talk • contribs) 14:19, 4 July 2012 (UTC)


 * I see your point, but you should only make a change if you have a good source. I'll look for some authoritative pronouncement on the subject of whether logic is a study or that which is studied.Rick Norwood (talk) 15:49, 4 July 2012 (UTC)


 * The idea that logic is the study of (some kinds of) argument is well-established. See Definitions of logic.  There isn't much of a paradox here: logic is primarily a study of arguments, but it is also the name we give to systems of inference that arise from that study.
 * I do find myself visiting these talk pages mostly to point out how the logic article has been in slow decline since 2009, and feel apologetic for that, but compare the lede from https://en.wikipedia.org/w/index.php?title=Logic&oldid=300599816 to that of the current article: that both better avoided making needless assertions (the substantial assertion it does make not now made is that formal systematic study of argument begins in Ancient Greece, not India or China), and did a better job of delivering the things a lede should deliver, such as a clear definition of the topic matter. &mdash; Charles Stewart (talk) 13:46, 13 August 2012 (UTC)

Logical Absolutes
Should this topic be discussed ? https://school.carm.org/amember/files/demo3/2_logic/absolutes.htm i think that its something that could be included in this topic, otherwise maybe it should have its own page Aperseghin (talk) 15:20, 14 August 2012 (UTC)
 * NOTE it seems to be touched on here http://en.wikipedia.org/wiki/Law_of_thought Aperseghin (talk) 15:23, 14 August 2012 (UTC)

My logic (Open to debate)
Under Construction...

Science(knowledge), is acquired by all the entities in the diagram.

Philosophy (love of wisdom), I believe 'love of wisdom' is inherent in acquiring knowledge, as otherwise, there is no reason to want knowledge. To get knowledge, you must first, have wanted it, in the first-place. (the purpose/knowledge wanted is irrelevant)

In an abstract way, (although the concepts are already abstract...) to have knowledge, you must at least have be able to 'know' something...or, anything... What is something/anything? The/a universe - what makes up a universe? The universe is made up of, 'physics', and 'meta-physics'.      (MST UPDATE)

Which I then class into two separate forms of base-logic. Rational-logic, and irrational-logic. or intelligence, or intellect... (MST UPDATE)

My source? Hopefully, the people of Wikipedia see it as credible...

— Preceding unsigned comment added by Wickid123 (talk • contribs) 12:47, 15 September 2012 (UTC)

What are you tripping on? How does this differ from Kant's boring old ancient analytic-synthetic distinction? Have you just changed some words around and added two differently spelled synonyms "intellect" and "intelligence" like you're bloody Derrida or summat? — Preceding unsigned comment added by 192.155.82.44 (talk) 06:26, 4 February 2013 (UTC)

I love logic and simply being here on Earth as a savvy human
Logic is how we humans think. If it is not logical, then it is questionable. Thanks.96.48.152.145 (talk) 07:41, 15 November 2012 (UTC)

Rejecting Logical Truths
I have to say I kind of disagree with some of the policies that wikipedia encourages for this article, verifiability in particular (not a fan of Popper). I have also, unintentionally overridden the discussion that has been going on behind the scenes here by just editing. So I am posting this to give yall a heads up and to say sorry, please edit my writing, but at least take it into account.

I was reading the bit at the end of Rejecting Logical Truths and I was really disappointed with the critiques given of Nietzsche. They were clearly partisan and I think the tone and content was pretty weak. Ive gone ahead and responded to each critique. I got quite angry with the Russell one in particular so that should probably be changed. But still i think this really needs to be looked at because the way it stood it seemed like some kind of definite rejection of the rejection but which is not convincing at all.

I also offered my kind of interpretation which I think would stem from a kind of positivistic attitude although i myself am really into the whole frankfurt critique of instrumental rationality and the positivists that are associated with that... So ye im also against imparciality. I think the article should vehemently argue for the competeing positions but allow them all up there! This may look contradictory but im all about paraconsistency!

Lots of love! — Preceding unsigned comment added by 192.155.82.44 (talk) 06:22, 4 February 2013 (UTC)

Mathematical/Symbolic/Formal Logic
The first section under "The study of logic" divides logic into four categories: informal, formal, symbolic and mathematical, whereof all but the first links to mathematical logic, where they are listed as synonyms. It also seems to be more confusion over these three terms later in the article. I'm not sure exactly what are the most recognized relationship between these terms, but we need to try to make it more consistent. –St.nerol (talk) 17:42, 27 May 2013 (UTC)


 * As it stands, that section only provides references to the content of each of the four categories, not to the fact that there are four categories. We need a broader reference.  In my experience, the examples are good ones, but we need a reference that says so.  In any case, while all mathematical logic is formal, not all formal logic is mathematical.  Some formal logic is Aristotelian. Rick Norwood (talk) 13:03, 28 May 2013 (UTC)

Circular reference
Logic refers to Reason, Reason loops back to Logic. Right in the first sentence in both cases. I understand, these are hard to define. But someone have to try harder. Thanks! :) — Preceding unsigned comment added by 98.204.176.240 (talk) 11:48, 2 June 2013 (UTC)

limits
the original article discuss logic from a non-scientific method of view which makes it hypothesis and as hypothesis its not suitable for practical purposes. if somebody interested in this article from a scientific method point of view please send me an email. — Preceding unsigned comment added by 2602:306:2403:E989:9D97:9A63:C19E:C76D (talk) 15:42, 22 August 2013 (UTC)

My Book is now an Author in Facebook - Is my Book still to be considered as not History ?
Please simply consider to be published as article after "SO MANY YEARS of first publishing", would be more logical for what is considered as a TAG as "Original Work"! THANKS!

My facebook Authors page is: https://www.facebook.com/BookPureLogic ! First published Canada 2008; USA 2009. So plus 10 years would make it 2018 and 2019, before WIKIPEDIA could consider the article about my Book! IS THIS SENSIBLE? THANK AGAIN! (General concensus2012 (talk) 22:05, 1 January 2015 (UTC))


 * Your book does not meet Wikipedia notability criteria - we aren't here to provide free promotion. AndyTheGrump (talk) 22:34, 1 January 2015 (UTC)


 * I agree with AndyTheGrump above the book is hardly on logic as "the use and study of valid reasoning". I had a look at your book at amazon, I could not read the bibliography or index, but what I did see didn't impress me, which chapters are over syllogisms or predicate logic WillemienH (talk) 00:31, 6 January 2015 (UTC)


 * Our personal opinions of books aren't really relevant though. What matters is whether they meet our notability criteria - and for that we'd need to see significant coverage in third-party published reliable sources, for a start. AndyTheGrump (talk) 01:35, 6 January 2015 (UTC)

Update Information
Most of the sources sited have been out dated, I believe it would be better to update some of its definitions from new books, to name a few:

"Logic- is the study of methods for evaluating whether the premises of an argument adequately support its conclusion." "Sound Argument- a valid argument in which all of the premises are true." "Valid Argument- one in which is necessary that, if the premises are true, then the conclusion is true." Source: Santiago. LOGIC CUSTOM. McGraw-Hill Create (tm). p. 66. ISBN 9781308201979. 14:49, 9 February 2015‎ HalleyRoséM


 * I could not agree with that, given that you are mostly thinking in terms of deduction. SaundersLane (talk) 21:49, 1 November 2015 (UTC)

What is first? Science or Logic?
Merriam-Webster Dictionary Main Entry: logic 1 : a science that deals with the rules and tests of sound thinking and proof by reasoning;

2 : sound reasoning 3 : the arrangement of circuit elements for arithmetical computation in a computer

http://dictionary.reference.com/ 1. the science that investigates the principles governing correct or reliable inference. 2. a particular method of reasoning or argumentation: We were unable to follow his logic. 3. the system or principles of reasoning applicable to any branch of knowledge or study. 4. reason or sound judgment, as in utterances or actions: There wasn't much logic in her move. 5. convincing forcefulness; inexorable truth or persuasiveness: the irresistible logic of the facts.

What is first or of higher level as to which is needed first? Is it the problem of the Hen and the Egg? Can Science be without logic? Yes it can, though it should not happen! Can logic be without Science? No and Yes! Logic and true "sound" reasoning, is Science! But good reasoning logic can be by itself, and not be Academic recognized Science! Though generally good sound reasoning logic, does proceed from much Science, theoretical and practical learning!

So half truths and half logic, or not complete logic, can or have been made Science in a few cases! But this does not happen to true complete(pure) logic!

Hence I would establish LOGIC and "complete/pure logic", thought, ideas, imagination, to be first, as the "software" and "hardware" of a computer! That then can be established in firm accepted Academia Science, with "strict" Rules and Laws developed(particular specific sciences) and that can be experimented and proven!

Much of Logic and "metaphysics", does not have to be proven as Science might apparently require! The power of Inference and Deduction enter into the game of sound reasoning or illogical reasoning!

If this is helpful, please feel free to use it! Thanks! (--General concensus2012 (talk) 04:58, 28 March 2013 (UTC))

I completely agree...! Back from exile 2013...! GeorgeFThomson (talk) 05:54, 22 July 2014 (UTC)]

Sometimes I am convinced this World does not take history records of what is "biased" as original work! When Original work should not be blocked as to making reference to it in a concise manner! GeorgeFThomson (talk) 05:58, 22 July 2014 (UTC)

Fuck David Kevin (talk) 04:15, 28 January 2016 (UTC)

The "types of logic" section
That section needs much better logic, in fact. I am surprised by its current state. Clearly, "Is logic empirical?" is not a type of logic, neither is "Rejection of logical truth". The basic concepts such as deductive vs inductive logic etc. are lost in a form of "spaghetti logic" in that section, I am afraid. SaundersLane (talk) 21:49, 1 November 2015 (UTC)


 * Some more items:


 * Given that the pages on Predicate logic and Propositional calculus both clearly state that they are subfields of Mathematical logic they can not be in the same level as that and are not "types of logic" as such if mathematical logic is considered a type.


 * Principle of bivalence is a "principle" as it says. It is not a type of logic. Neither is "Rejection of logical truth" which is now 3 paragraphs here as a form of "rambling logic". It really needs to go at the end to a subsection of its own called truth and logic or something, and become much shorter.


 * Overall many, many problems remain here. SaundersLane (talk) 00:14, 2 November 2015 (UTC)


 * This section used to be two parts, a 'types of logic' section and a 'controversies in logic' section. The latter was removed, I assume by some drive-by editor who had a thing against controversies sections and was not interested in the coherence of the article.  The logic article has suffered a great deal from these kinds of issue since 2009. In the medium term, the article badly needs an overhaul, but as a stop-gap, the division could be reinstated. &mdash; Charles Stewart (talk) 10:43, 16 March 2016 (UTC)
 * I've reinstated the controversies in logic section and added a new subsection on material inference. &mdash; Charles Stewart (talk) 12:31, 16 March 2016 (UTC)

Overhaul
I want to put some energy into solving a number of issues with the article as it stands. The article has not impoved much since 2005 and has become weaker in a number of areas, so one of the things I will be doing is going over the differences in https://en.wikipedia.org/w/index.php?title=Logic&diff=cur&oldid=28701908 and restoring the older text where it is clearer or more correct than the current version. &mdash; Charles Stewart (talk) 14:10, 16 March 2016 (UTC)

Peter Damian's old plan for the article is at User:Peter Damian/logic. &mdash; Charles Stewart (talk) 10:12, 17 March 2016 (UTC)

Illogicality (part of "thought disorder") and Schizophrenia
Thought disorder links here (probably unintentionally?) via a redirect through "illogicality" into "logic".

Illogicality as a symptom of a mental disorder is a relatively concrete and narrow thing that is *somewhat* related to high church "Logic", but it is also importantly distinct.

I think a better arrangement would to EITHER (1) have a full article for Illogicality as a symptom instead of the current redirect OR (2) there should be a subsection in this article about Illogicality as a symptom of thought disorder.

A good template for how Illogicality should look (whether as a section or a whole article) is the Alogia article which covers a related symptom. — Preceding unsigned comment added by 2620:0:100E:903:506C:9E8:7BB4:79C5 (talk) 22:48, 16 February 2016 (UTC)
 * The article could have a section on logic and rationality, with a subsection title Illogicality that documents this condition. Would this be a good thing? &mdash; Charles Stewart (talk) 10:50, 16 March 2016 (UTC)


 * I've changed ‎the title of the Deductive and inductive reasoning, and abductive inference subsection to Logic and rationality, which now needs rewriting and can now discuss alogia/illogicality. &mdash; Charles Stewart (talk) 06:51, 6 April 2016 (UTC)


 * I've created an article as the main article of the Logic and rationality subsection, and am about to start adding a discussion of illogicality. &mdash; Charles Stewart (talk) 07:07, 11 April 2016 (UTC)

Questions
"A valid argument is one where there is a specific relation of logical support between the assumptions of the argument and its conclusion. " I remember saying something like this. Do any other textbooks mention this? The standard one is 'premises not true with conclusion false'. Peter Damian (talk) 07:35, 1 May 2016 (UTC)

[edit] I wrote “A valid argument is one where there is a connection between the assumptions of the argument and its conclusions that is informally signified by words like 'therefore', 'hence', 'ergo' and so on.”  ‘Connection’ was changed to ‘specific relation of logical support’. Peter Damian (talk) 07:38, 1 May 2016 (UTC)

Noting that User:Jbessie is Professor of Philosophy at University of Wisconsin-Stout whose interests include mathematical logic, the philosophy of science etc, so presumably knows what he is talking about! I think the intro reads fine. Peter Damian (talk) 07:40, 1 May 2016 (UTC)


 * Thanks for your recent work on the article. &mdash; Charles Stewart (talk) 11:03, 2 May 2016 (UTC)

Good article status
I'd like us to get the article into shape to nominate it for good article status. There are a few things that need to be done before we nominate it:

1. The readability of several sections could do with improvement.

2. The article needs to be better referenced.

3. The article could use a few more illustrations.

I value all assistance with these.&mdash; Charles Stewart (talk) 11:03, 2 May 2016 (UTC)
 * Illustrations for logic? I will try and put some time aside for the words. Peter Damian (talk) 17:42, 2 May 2016 (UTC)
 * Propositional logic lends itself naturally to illustration by Venn diagrams and predicate logic by analogy can be illustrated with one of Peirce's existential graphs. Term logic could be illustrated with the square of opposition. &mdash; Charles Stewart (talk) 18:16, 2 May 2016 (UTC)

Readability
"According to the modern view, the fundamental form of a simple sentence is given by a recursive schema, involving logical connectives, such as a quantifier with its bound variable, which are joined by juxtaposition to other sentences, which in turn may have logical structure."

What does this mean? Peter Damian (talk) 17:46, 2 May 2016 (UTC)

(I think what it is getting at is that instead of a fixed two-term + copula structure, we now have a flexible structure where sentences can embed other sentences etc. The trick is to explain this to the average reader such as myself). Peter Damian (talk) 17:48, 2 May 2016 (UTC)

I think it may be better to reverse the order of the bullet points, starting with 'the modern view is more complex', then showing how the simple predicate analysis of the Aristotelian sentence can expand outwards indefinitely. Peter Damian (talk) 17:50, 2 May 2016 (UTC)
 * I've changed the order in which the concepts are introduced: hopefully the text is now easier to digest. &mdash; Charles Stewart (talk) 06:23, 3 May 2016 (UTC)

Confucius
Please remove the photo of Confucius. He was NOT a logician. What is his contribution in logic study? — Preceding unsigned comment added by Logicmind7 (talk • contribs)
 * The photo of Confucius is not there because he is a logician. It's there because this article is part of the series of philosophy-related articles. That image was made to be placed in all articles of the series. Amccann421 &#160; (talk)  03:29, 9 June 2016 (UTC)


 * Thanks for reply, the problems is that ..... He was NOT a logician, and he was NOT a great philosopher.
 * There were many greater logicians and philosophers. — Preceding unsigned comment added by Logicmind7 (talk • contribs) 15:36, 29 June 2016 (UTC)


 * Please sign all your talk page messages with four tildes ( ~ ) and indent the messages as outlined in wp:THREAD and wp:INDENT. Thanks.
 * But greatness is not required to have your picture in Wikipedia. I think the best thing you can do, is leaving a message and hoping to get a discussion started at Template_talk:Philosophy_sidebar. Good luck! - DVdm (talk) 15:45, 29 June 2016 (UTC)
 * Here is a philosophical question: What constitutes a great philosopher? Dhrm77 (talk) 16:56, 29 June 2016 (UTC)
 * Erm... being there when there just happens to be lack of great scientists to really answer the questions at hand? - DVdm (talk) 17:14, 29 June 2016 (UTC)

Personal logic
Usually the term "personal logic" means differentiation from the norm supposedly positive for the believer as he/she claims. Personal logic thinkers usually have very low iq test performance because they don't try to understand the cosmos, even if they claim so, simply to simplify the cosmos in order it fits inside their small brains. Physicists for example might have different opinions, but they don't try to create a personal logic, but to understand the actual world. Neuroscientists and psychologists study the aspects of personal logic, not to believe in it, but in order they understand the brain. Personal pseudo-logicians claim that their views are rare and unique, because there are infinite ways to be wrong than try to be reasonable. Personal logic isn't something rare or unique statistically though, even if the quasi-thinkers claim so. Everyone has partially an apparent "personal logic", but the term means shallow causal and biased thinking. — Preceding unsigned comment added by 2A02:587:410D:7800:C87:6EB1:1B01:90D7 (talk) 22:10, 6 October 2016 (UTC)


 * Couldn't find any sources on the term, can you provide any? Paradoctor (talk) 22:34, 6 October 2016 (UTC)
 * https://www.matrixwissen.de/index.php?option=com_content&view=article&id=808:what-relevance-does-my-personal-logic-have-with-respect-en&catid=204&lang=en&Itemid=794
 * but this researching dialogue isn't yet complete — Preceding unsigned comment added by 2A02:587:410D:7800:C87:6EB1:1B01:90D7 (talk) 22:53, 6 October 2016 (UTC)
 * Content to be added must be supported by reliable sources, this doesn't qualify. Paradoctor (talk) 01:10, 7 October 2016 (UTC)

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Valid inference
"A valid inference is one where there is a specific relation of logical support between the assumptions of the inference and its conclusion"

I don't think this explains much, because "logic" was previously defined in terms of inference. So, it ends up being circular. The best definition of logic I've heard is the study of "truth-preserving inference." — Preceding unsigned comment added by Bsharvy (talk • contribs) 19:03, 9 November 2019 (UTC)


 * Edited. Thanks to you for pointing out that issue. Fabio Maria De Francesco (talk) 15:28, 20 December 2019 (UTC)

Strenge Logik by Walther Brüning
Hello!

There had been a german logician, who was able to explain logic good. (I don't know whether he is still alive. I don't think so.) I think he is not very famous, but I don't know why. The pitty for english-speaking people, who are accidently interested in his theory, is, that his book "Grundlagen der strengen Logik" is only available in german. So if you are interested, here is a part of his work: https://en.wikipedia.org/w/index.php?oldid=842329272#Strict_syllogistic

I really think he is right with every single word, but i don't dare to change the article for logic. I am curious about your opinions.

--123qweasd (talk) 17:03, 5 October 2020 (UTC)

Copyright problem removed
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Philosophical logic not displaying title
Does anyone know why the Philosophical logic section doesn't display the title just below the citation box? -Theklan (talk) 10:14, 14 January 2021 (UTC)
 * I'll look at it. My guess is that it is something to do with the Peirce quote box: these have tricky behaviours. &mdash; Charles Stewart (talk) 07:52, 15 January 2021 (UTC)
 * I think I fixed it by changing the quote box alignment from left to center - as far as I can tell the quote box looks exactly the same, but the missing title now shows up. Burritok (talk) 07:38, 12 March 2021 (UTC)

Added Persia, to ancient civilizations studying logic.
I think Avicienna's Contribution to the study of logic, makes persia relevant. In fact, that makes all Muslim philosophers relevant. The main article unfairly makes no mention of any Muslim philosopher.


 * The history section used to have a paragraph on medieval Islamic logic which was deleted without reason in 2019, which I have reinserted together with a sentence indicating the influence of Islamic logicians on Christian logicians in medieval times. I don't think the fact that Avicenna was Persian is any more relevant to this article than the fact that, say Abelard was French. &mdash; Charles Stewart (talk) 11:22, 6 July 2021 (UTC)

May chapter 4 Types be combined to chapter 1?
There are redundancy between chapter 1 and 4. May chapter 4 Types be combined to chapter 1 as below?

Chapter 1	Types of logic --Gluo88 (talk) 00:00, 2 July 2021 (UTC)
 * 1) 	Philosophical logic
 * 2) 	Informal logic
 * 3) Informal reasoning and dialectic
 * 4) 	Formal logic - classical logic
 * 5) Mathematical logic
 * 6) Syllogistic logic
 * 7) Propositional logic
 * 8) Predicate logic
 * 9) Computational logic
 * 10) 	Formal logic- Non-classical logic
 * 11) Modal logic
 * There's a problem here, but I don't think this solution would be good. Modal logic was treated informally and philosophically by Aristotle, received a formal treatment by the Muslin logicians, an axiomatic treatment in the C19th and finally a treatment in mathematical logic with the advent of Kripke semantics. It spans all of what were called the "types of logic". Likewise, there is a prejudice among some logicians, made popular by Quine, that logics like S4 are non-classical because the modal operators cannot be given a truth-conditional semantics, but as a matter of fact modal logicians distinguish between classical and non-classical modal logics, based on whether they are most naturally given a bivalent semantics.
 * I think it has been a strength of the current article that it outlines fundamental concepts like logical form and semantics before getting into specialist logical concepts like classical-strength axiomatisations and modality - we have to thank for arguing that we should do this and actually putting together the first four of these sections. I think it would not be possible to carry out something along the lines you propose without violating this, in which case I am opposed to the proposal.
 * I tend to agree Peter Damian (talk) 21:29, 2 July 2021 (UTC)
 * I think I am guilty of introducing the subheading "Types of logic", which is a bad name. I've renamed it to "Approaches to logic", which I am not attached to but find definitely less bad. "Aspects of logic" might also be better. &mdash; Charles Stewart (talk) 08:50, 2 July 2021 (UTC)

@Charles Stewart, thank you very for your explanation. It looks to me that "Approaches to logic" is a better term too. --Gluo88 (talk) 17:39, 2 July 2021 (UTC)
 * Do you think that it might be better also to change Philosophical logic, Informal logic in Chapter 1, ..., to Philosophical approach, Informal approach, ..., for distinguishing them from the concepts of Philosophical logic, Informal logic in chapter 4?
 * May Classic approach (corresponding to the concept of Classical logic) be added to the outline chapter (chapter 1) since it looks to be an important concept in logic literature?
 * I'm not attached to the wording at all. The terms 'philosophical logic', 'informal logic', etc. are well-established terms of art, which trumps the issue of being consistent here.
 * I think it is probably a good idea to have a subsection devoted to introducing the idea of classical logic that appears before the subsection on non-classical logics. Maybe the place to have it would be to add a section 'Negation, contradiction and classical logic' to the Concepts section. Something not widely appreciated is that classical logic is not 'classical' in that it does not date back to antiquity: while the principle of excluded middle was accepted by ancient logicians, the principle of explosion was not and both Aristotelian and Stoic logicians accepted principles that cannot consistently be added to classical logic. See connexive logic. &mdash; Charles Stewart (talk) 18:29, 2 July 2021 (UTC)
 * Yes,  you are right on the issue of being consistent here. I just feel that the same term should have  identical meaning, but it looks that a term for an approach in chapter 1 is also a type in chapter 4, a little different?
 * I support the idea of having a subsection devoted to introducing the idea of classical logic that appears before the subsection on non-classical logics.
 * Yes, I agree with you that "Something not widely appreciated is that classical logic is not 'classical' in that it does not date back to antiquity". Does Wikipedia Aristotelian logic page capture the logic with Aristotelian principles (excluding principle of explosion)? If so, may another subsection (Aristotelian logic) devoted to this type logic (one type of non-classical logic)?
 * Thanks a lot. --Gluo88 (talk) 20:42, 2 July 2021 (UTC)
 * The Term logic page says very little about Aristotle's theory of propositions, which is reasonable since Aristotle's formal theory is a theory of syllogisms; the principle of explosion does not apply to syllogistic theories, since they have no unused premises. The formal content of Aristotleian logic is really very dissimilar to the propositional and predicate logics that are today called classical; Stoic logic, which is a kind of propositional relevance logic, resembles modern logic rather more. The problem is that while there's lot that I could say about the similarities and dissimilarities between modern and ancient logic, we can't just write what we think is true but we have to keep to only that which we can back up with reliable sources.
 * That doesn't stop us introducing classical logic earlier than we do. It's really just a matter of deciding what the most natural place to do so is. I've been thinking about this but not come up with a plan I am altogether happy with. &mdash; Charles Stewart (talk) 19:10, 5 July 2021 (UTC)
 * Thanks a lot for your explanation. Is there any issue for putting both classical logic and non-classical logic just in chapter 1?--Gluo88 (talk) 01:23, 7 July 2021 (UTC)

Wow! What happened to the article?
I'm talking about https://en.wikipedia.org/w/index.php?title=Logic&action=historysubmit&type=revision&diff=1039487529&oldid=1032265705

It's been a long time since the article changed so much, so quickly. Could I have an explanation for where this is all going? &mdash; Charles Stewart (talk) 19:37, 19 August 2021 (UTC)


 * Hi! Reader-friendliness was the main concern behind the changes that I made. The earlier version had a lot of fantastic stuff in it, but it wasn't the sort of thing I felt I could send to my non-logician friends and say "this is what the field is about". For instance, the section on modal logic had only covered its development and its application to natural language, so I added a concise 101-style explanation of what it actually is and the role it plays in the field. Most of my changes were similar, and made for similar reasons. Of course, I'm happy to discuss if you disagree with anything! Botterweg14  (talk)  22:13, 19 August 2021 (UTC)


 * I replied to this at the time, but the internet swallowed my response and I lacked the motivation to reply again. I do not recall what I wrote, but I recall thinking that, while I neither liked the changes in general nor understood what drove the individual choices made, it was good that somebody, at long last, was putting energy into improving the article.
 * Since then, I have lost interest in trying to maintain the article. The same thing that occurred during my years of semi-retirement is happening to the article again: there is no consensus among the active editors about what form the article should take, and so there are scuffles over decisions where there had earlier been consensus.
 * Wikipedia does offer one avenue to protect reasonable quality articles from this otherwise normal process of deterioriation: articles that achieve "good article" status are monitored to ensure that subsequent changes are improvements. Unfortunately, it is hard to get high importance articles through the good article process.
 * I'd like us to revisit the changes Botterweg made. Are they improvements? Can we achieve a common view of what the article should look like? Can we get the article to good article status? &mdash; Charles Stewart (talk) 06:37, 30 December 2021 (UTC)
 * I would be very glad to help get the article to good article status, and once again I'm happy to discuss if you have any specific disagreements about my edits. Botterweg14  (talk)  07:07, 30 December 2021 (UTC)

Shortdesc vs hatnote
The shortdesc for this page defines the subject as "The study of inference and truth," while the hatnote has "the systematic study of the form of arguments." These strike me as pretty different things, so I thought I'd point it out here in case any subject experts want to alter one. -- asilvering (talk) 17:56, 17 November 2021 (UTC)
 * Thanks, I switched in favor of the shortdesc. The two aren't really that different, but the shortdesc gives a more general characterization. Botterweg14  (talk)  22:45, 17 November 2021 (UTC)
 * The two are, in fact, very different. They represent rival, incompatible views on the subject matter of logic. Few logicians think their subject encompasses the study of truth in its broadest sense. &mdash; Charles Stewart (talk) 06:19, 30 December 2021 (UTC)
 * I agree with User:Charles Stewart that "the study of truth" is too broad as a characterization of logic. For example, all the theories of truth are usually not directly studied when studying logic. I would suggest to use "Study of correct reasoning" since this is more specific but still broad enough to capture both formal and informal logic. Phlsph7 (talk) 13:46, 30 December 2021 (UTC)
 * I can live with that for the shortdesc, but I do think the article itself needs to lean in the direction of "big tent" (while summarizing more specific conceptions of the topic, as in the current version). Botterweg14  (talk)  19:27, 30 December 2021 (UTC)
 * @Phlsph7 @Botterweg14 What about simply "study of reasoning"? Again, I'm a non-expert, so I'm not sure if that is no good for some reason, but it seems better to me than "study of correct reasoning" from a big-tent perspective. -- asilvering (talk) 20:21, 30 December 2021 (UTC)
 * The "study of reasoning" belongs to psychology since it includes good and bad reasoning. See for example the first paragraph of Philosophy_of_logic. So we need a qualifier like "correct", "good", or "valid". We could use "arguments" or "thinking" instead of "reasoning". Phlsph7 (talk) 20:30, 30 December 2021 (UTC)
 * The word "correct" is definitely doing some key work here as @Phlsph7 points out, so I'd favour just leaving it as is. Any shortdesc-length definition is gonna be reductive, and I think "study of correct reasoning" is an acceptable balance of tradeoffs. Botterweg14  (talk)  20:51, 30 December 2021 (UTC)

Content removed from section "Definition"
Hello User:Botterweg14 and thanks for your efforts at improving this article earlier this year. I saw that you removed 2 full paragraphs from the section "Definition" in your recent series of edits. I'm not sure that this removal was intentional since it was not even mentioned in your edit summaries. If it was, I would ask you to explain your reasons for the full removal. The removed material talks about very general characteristics of logic, different approaches to defining it, and different ways the term is used. It is therefore clearly relevant to the section "Definition". The material is also well-sourced. The paragraphs in question are:

"These general characterizations apply to logic in the widest sense since they are true both for formal and informal logic. But many definitions of logic focus on formal logic because it is the paradigmatic form of logic. In this narrower sense, logic is a formal science that studies how conclusions follow from premises in a topic-neutral way. As a formal science, it contrasts with empirical sciences, like physics or biology, because it tries to characterize the inferential relations between premises and conclusions only based on how they are structured. This means that the actual content of these propositions, i.e. their specific topic, is not important for whether the inference is valid or not. This can be expressed by distinguishing between logical and non-logical vocabulary: inferences are valid because of the logical terms used in them, independent of the meanings of the non-logical terms. Valid inferences are characterized by the fact that the truth of their premises ensures the truth of their conclusion. This means that it is impossible for the premises to be true and the conclusion to be false. The general logical structures characterizing valid inferences are called rules of inference. In this sense, logic is often defined as the study of valid inference. This contrasts with another prominent characterization of logic as the science of logical truths. A proposition is logically true if its truth depends only on the logical vocabulary used in it. This means that it is true in all possible worlds and under all interpretations of its non-logical terms. These two characterizations of logic are closely related to each other: an inference is valid if the material conditional from its premises to its conclusion is logically true."

"The term 'logic' can also be used in a slightly different sense as a countable noun. In this sense, a logic is a logical formal system. Different logics differ from each other concerning the formal languages used to express them and, most importantly, concerning the rules of inference they accept as valid. Starting in the 20th century, many new formal systems have been proposed. There is an ongoing debate about which of these systems should be considered logics in the strict sense instead of non-logical formal systems. Suggested criteria for this distinction include logical completeness and proximity to the intuitions governing classical logic. According to these criteria, it has been argued, for example, that higher-order logics and fuzzy logic should not be considered logics when understood in a strict sense."

Regards, Phlsph7 (talk) 06:08, 30 December 2021 (UTC)


 * Hey there, and thanks for your improvements as well! I think all of the information you added is useful for the article, but I think it gets too deep into nitty-gritties and controverseys for that particular section. So I was trying to rehome the information elsewhere (e.g. a new subsection for logical truth, a note in the "formal systems" section on the term "a logic") and in the process of doing that noticed that some topics were already covered elsewhere (e.g. definition of validity). But I may have screwed up somewhere so please do readd anything you think I deleted in error! Botterweg14  (talk)  07:02, 30 December 2021 (UTC)


 * I went ahead and restored the deleted paragraphs. I agree that redundancy is to be kept to a minimum but it's often necessary to a degree since the reader of one section usually can't be expected to have a full familiarity with the contents explained in detail in another section. I think the short definition of validity is necessary here so the reader can understand the difference between "logic as the science of valid inference" and "logic as the science of logical truth". But maybe there is a more concise formulation to further reduce the redundancy. Phlsph7 (talk) 07:28, 30 December 2021 (UTC)

Changes to sections "Definition" and "Formal and informal logic"

 * I see your point there. The classic "X is hard to explain without presupposing knowledge of Y but Y is hard to explain without presupposing X" trap! Here's one possible alternate formulation that preserves almost all of your text but I think is more navigable for readers without much background in logic. We can discuss, but please also feel free to edit in my sandbox or in the article, or whatever you think will keep the article progressing most efficiently. Botterweg14  (talk)  19:08, 30 December 2021 (UTC)


 * I think your expanded introductory paragraph works fine. I made a small copy edit. I'm fine with adding your first paragraph to replace the current first paragraph. I have been working on a rewrite of the section "Formal and informal logic". I still need more time to finish it but this is the current state, without polish or sources. There are still some open questions, like how to integrate the current material of the section into it.


 * I think it makes more sense to have the section "Formal and informal logic" as a separate section, as it was before, since the different ways of how to distinguish formal and informal logic don't directly pertain to the definition of logic in general. But since the term logic is often used synonymously with formal logic, it makes sense to keep the current characterization in the definition section. If you don't mind to wait a day or two then I should have it finished and then we can decide how to best split the material among the sections. Feedback on the current draft is appreciated and feel free to edit as well if you see ways to improve it. Phlsph7 (talk) 19:55, 30 December 2021 (UTC)


 * Cool, I'll sit on that and we'll talk when your rewrite is ready. I agree that it would be better to relocate the informal vs formal stuff so long as the text in that section doesn't presupose it as background information, and that seems to be the tack you're taking. I like what you've put in the sandbox, and my only overall comment is that I think more concrete examples would be helpful for readers without much background knowledge. I've put some suggestions along those lines in a separate section of your sandbox. Botterweg14  (talk)  20:30, 30 December 2021 (UTC)


 * Thanks for the feedback. I'll try to incorporate your examples. Phlsph7 (talk) 20:42, 30 December 2021 (UTC)


 * Awesome, though I'm not at all attached to the particulars of my examples so feel free to change or adapt them. I just think some sort of examples would make things more concrete and thus help naive readers get from "yikes what's this mumbo jumbo" to "okay, I see what's going on here this stuff is cool". Botterweg14  (talk)  20:54, 30 December 2021 (UTC)

I finished the draft of the section "Formal and informal logic". I used your example for the language-based distinction. For the context-dependence, I decided to expand the strawman example already present in the text. My suggestion is to use this section as a replacement for the current subsection "Formal and informal logic" but turn it again into a main section. The section "Definition" would then only have 3 paragraphs, for which a further subdivision wouldn't be necessary. But it would still profit from the changes to its introductory paragraph you proposed. Phlsph7 (talk) 17:28, 31 December 2021 (UTC)

I went ahead and made the suggested changes. Feel free to let me know your thoughts once you have time again. Phlsph7 (talk) 07:57, 2 January 2022 (UTC)


 * Awesome! I might eventually have nitpicks here and there but I like the changes and they definitely improve the article! Botterweg14  (talk)  20:04, 5 January 2022 (UTC)

"Logika" listed at Redirects for discussion
An editor has identified a potential problem with the redirect Logika and has thus listed it for discussion. This discussion will occur at Redirects for discussion/Log/2022 February 12 until a consensus is reached, and readers of this page are welcome to contribute to the discussion. User:1234qwer1234qwer4 (talk) 02:18, 12 February 2022 (UTC)