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Existence article draft 2
The study of existence is a branch of philosophy known as ontology.

Many questions arise concerning existence. Is what we experience and observe all there is to existence? Do abstract ideas, such as virtue, exist? Is existence orderly and knowable or chaotic and unknowable? Does there exist an external reality that is completely ontologically independent of our conceptual schemes, linguistic practices, and beliefs?

Plato, in the Republic, argued that existence was the world of ideas, and that our everyday lives are but dim shadows of this eternal reality. Aristotle considered that existence was made up of form and substance, and was discovered by the senses. Heraclitus said that existence is change. Descartes argued that we can be absolutely certain of the existence of our own conscious awareness.

Philosophers and mathematicians who study logic use the symbol ∃ to denote the existential quantifier, which asserts the existence of some object with certain properties.

History
In the Hindu religion, existence is a dream of Brahma. Existence can be seen as central to many systems of belief, religions, and myths. Beliefs concerning existence may posit additional properties, such as value or goodness. Divergent conceptions of existence have often resulted in tension amongst communities with differing beliefs about existence, especially when coupled with the related question of worldview.

In the western tradition of philosophy, the first comprehensive treatments of the subject are from Plato's Phaedo, Republic, and Statesman and Aristotle's Metaphysics, though earlier fragmentary writing exists. Aristotle developed a complicated theory of being, according to which only individual things, called substances fully have being, but other things such as relations, quantity, time and place (called the categories) have a derivative kind of being, dependent on individual things.

The Neo-Platonists and some early Christian philosophers argued about whether existence had any reality except in the mind of God. Some taught that existence was a snare and a delusion, that the world, the flesh, and the devil existed only to tempt weak humankind away from God.

The medieval philosopher Thomas Aquinas, perhaps following the Persian philosopher Avicenna, argued that God is pure being, and that in God essence and existence are the same. At about the same time, the nominalist philosopher William of Ockham, argued, in Book I of his Summa Totius Logicae (Treatise on all Logic, written some time before 1327) that Categories are not a form of Being in their own right, but derivative on the existence of individuals.

Early modern
The early modern treatment of the subject derives from Antoine Arnauld and Pierre Nicole's Logic, or 'The Art of Thinking', better known as the Port-Royal Logic.

Arnauld thought that a proposition or judgment, consists of taking two different ideas and either putting them together or rejecting them:


 * After conceiving things by our ideas, we compare these ideas and, finding that some belong together and others do not, we unite or separate them. This is called affirming or denying, and in general judging.


 * This judgment is also called a proposition, and it is easy to see that it must have two terms. One term, of which one affirms or denies something, is called the subject; the other term, which is affirmed or denied, is called the attribute or Praedicatum.

The two terms are joined by the verb "is" (or "is not", if the predicate is denied of the subject). Thus every proposition has three components: the two terms, and the "copula" that connects or separates them. Even when the proposition has only two words, the three terms are still there. For example "God loves humanity", really means "God is a lover of humanity", "God exists" means "God is a thing".

This theory of judgment dominated logic for centuries, but it has some obvious difficulties: it only considers proposition of the form "All A are B.", a form which logicians call universal. It does not allow propositions of the form "Some A are B.", a form logicians call existential. If neither A nor B includes the idea of existence, then "some A are B" simply adjoins A to B. Conversely, if A or B do include the idea of existence in the way that "triangle" contains the idea "three angles equal to two right angles", then "A exists" is automatically true, and we have an ontological proof of A's existence. (Indeed Arnauld's contemporary Descartes famously argued so, regarding the concept "God" (discourse 4, Meditation 5). Arnauld's theory was current until the middle of the nineteenth century.

David Hume argued that the claim that a thing exists, when added to our notion of a thing, does not add anything to the concept. For example, if we form a complete notion of Moses, and superadd to that notion the claim that Moses existed, we are not adding anything to the notion of Moses. Kant also argued that existence is not a "real" predicate, but gave no explanation of how this is possible, indeed his famous discussion of the subject is merely a restatement of Arnauld's doctrine that in the proposition "God is omnipotent", the verb "is" signifies the joining or separating of two concepts such as "God" and "omnipotence".

Predicative nature of existence
John Stuart Mill (and also Kant's pupil Herbart) argued that the predicative nature of existence was proved by sentences like "A centaur is a poetic fiction" or "A greatest number is impossible" (Herbart). Franz Brentano challenged this, so also (as is better known) did Frege. Brentano argued that we can join the concept represented by a noun phrase "an A" to the concept represented by an adjective "B" to give the concept represented by the noun phrase "a B-A". For example, we can join "a man" to "wise" to give "a wise man". But the noun phrase "a wise man" is not a sentence, whereas "some man is wise" is a sentence. Hence the copula must do more than merely join or separate concepts. Furthermore, adding "exists" to "a wise man", to give the complete sentence "a wise man exists" has the same effect as joining "some man" to "wise" using the copula. So the copula has the same effect as "exists". Brentano argued that every categorical proposition can be translated into an existential one without change in meaning and that the "exists" and "does not exist" of the existential proposition take the place of the copula. He showed this by the following examples:


 * The categorical proposition "Some man is sick", has the same meaning as the existential proposition "A sick man exists" or "There is a sick man".


 * The categorical proposition "No stone is living" has the same meaning as the existential proposition "A living stone does not exist" or "there is no living stone".


 * The categorical proposition "All men are mortal" has the same meaning as the existential proposition "An immortal man does not exist" or "there is no immortal man".


 * The categorical proposition "Some man is not learned" has the same meaning as the existential proposition "A non-learned man exists" or "there is a non-learned man".

Frege developed a similar view (though later) in his great work The Foundations of Arithmetic, as did Charles Peirce. The Frege-Brentano view is the basis of the dominant position in modern Anglo-American philosophy: that existence is asserted by the existential quantifier (as expressed by Quine's slogan "To be is to be the value of a variable." &mdash; On What There Is, 1948).

The semantics of existence
In mathematical logic, there are two quantifiers, "some" and "all", though as Brentano (1838-1917) pointed out, we can make do with just one quantifier and negation. The first of these quantifiers, "some" is also expressed as "there exists". Thus, in the sentence "There exist a man," the term "man" is asserted to be part of existence. But we can also assert, "There exists a triangle." Is a "triangle", an abstract idea, part of existence in the same way that a "man", a physical body, is part of existence? Do abstractions such as goodness, blindness, and virtue exist in the same sense that chairs, tables, and houses exist? What categories, or kinds of thing can be the subject or the predicate of a proposition?

Worse, does "existence" exist? A statement should include a subject and a predicate. The statement, "Existence is not a predicate." is of the subject-predicate form. The statement "A bridge crosses the Thames at Hammersmith." cannot just be about a bridge, the Thames, and Hammersmith. It must be about "existence" as well.

The nominalist approach is to argue that certain noun phrases can be "eliminated" by rewriting a sentence in a form that has the same meaning, but which does not contain the noun phrase. Thus Ockham argued that "Socrates has wisdom", which apparently asserts the existence of a reference for "wisdom", can be rewritten as "Socrates is wise", which contains only the referring phrase "Socrates". This method became widely accepted in the twentieth century by the analytic school of philosophy.

However, this argument may be inverted by realists in arguing that since the sentence "Socrates is wise" can be rewritten as "Socrates has wisdom", this proves the existence of a hidden referent for "wise".

A further problem is that both a singular sentence like "Pegasus flies" and its negation seem to imply the existence of a subject. If "Pegasus flies" is true, then something (namely Pegasus) flies. So if the sentence is true, "Pegasus" has a referent. But if the sentence is false, its negation is true. But the negation of "Pegasus flies" is "it is not the case that Pegasus flies". If this is true, then something (namely Pegasus) does not fly, and so "Pegasus" still has a referent. Whether "Pegasus flies" is true or not, "Pegasus" has a referent. But common sense suggests that "Pegasus" does not have a referent. This is part of the larger problem with the existence of fictional objects. We need some way to be able to make statements about fictional objects without having our sentence declared either devoid of meaning or false.

Modern approaches
According to Bertrand Russell's Theory of Descriptions, the negation operator in a singular sentence takes wide and narrow scope: we distinguish between "some S is not P" (where negation takes "narrow scope") and "it is not the case that 'some S is P'" (where negation takes "wide scope"). The problem with this view is that there appears to be no such scope distinction in the case of proper names. The sentences "Socrates is not bald" and "it is not the case that Socrates is bald" both appear to have the same meaning, and they both appear to assert or presuppose the existence of someone (Socrates) who is not bald, so that negation takes narrow scope.

The theory of descriptions has generally fallen into disrepute, though there have been recent attempts to revive it by Stephen Neale and Frank Jackson. According to the direct-reference view, an early version of which was originally proposed by Bertrand Russell, and perhaps earlier by Gottlob Frege, a proper name strictly has no meaning when there is no object to which it refers.

This view relies on the argument that the semantic function of a proper name is to tell us which object bears the name, and thus to identify some object. But no object can be identified if none exists. Thus, a proper name must have a bearer if it is to be meaningful.

To adapt an argument of Peter Strawson's, someone who points to an apparently empty space, uttering "that's a fine red one" communicates nothing to someone who cannot see or understand what he is pointing to. Variants of the direct-reference view have been proposed by Saul Kripke, Gareth Evans, Nathan Salmon, Scott Soames, and others.

Wide and narrow scope
According to the "two sense" view of existence, which derives from Alexius Meinong, existential statements fall into two classes.


 * 1. Those asserting existence in a wide sense.  These are typically of the form "N is P" for singular N, or "some S is P".


 * 2. Those asserting existence in a narrow sense.  These are typically of the form "N exists" or "S's exist".

The problem is then evaded as follows. "Pegasus flies" implies existence in the wide sense, for it implies that something flies. But it does not imply existence in the narrow sense, for we deny existence in this sense by saying that Pegasus does not exist. In effect, the world of all things divides, on this view, into those (like Socrates, the planet Venus, and New York City) that have existence in the narrow sense, and those (like Sherlock Holmes, the goddess Venus, and Minas Tirith) that do not.

However, common sense suggests the non-existence of such things as fictional characters or places.

European views
Influenced by the views of Brentano's pupil Alexius Meinong, and by Edmund Husserl, Germanophone and Francophone philosophy took a different direction regarding the question of existence. Existentialism has been a major strand of continental philosophy in the twentieth century.