User:Francis Schonken/Don't use internal sources for verification

The central question of this essay is:"Can Wikipedia use itself, or any other Mediawiki project as a source?"The short answer to that question is: for article content generally not, at least not as a technique for acquiring a better compliance to Verifiability.

There are circumstances where Wikipedia can, and sometimes even should, indicate itself as a source: these circumstances then don't relate to Verifiability, but to the framework of copyrights in combination with the Gnu Free Documentation License that applies to Wikipedia, or, alternatively, the verified content is no part of the encyclopedia itself.

There are some differences regarding self-sourcing, depending on namespace: for that reason namespaces (or at least the content displayed in each namespace) are treated seperately in this essay.

Content displayed in Main namespace
It should generally be avoided to use one Wikipedia page for the verification of the content of another Main namespace Wikipedia page. Some principal reasons for that are:
 * 1) Wikipedia content is not above all suspicion reliability-wise: there was a relative success with the report published in Nature late 2005, but errors in Wikipedia are still legion. One of the tactics against systemic errors is not basing one part of a system on another, possibly erroneous, part of the same system: in that case an error might be reproduced within the same system, which would be turning a one time error into a systemic one.
 * 2) Avoid self-references: Self-references should be avoided for various reasons, one of these reasons is countering systemic bias. Systemic bias can be initiated, for instance, by circularity, that is articles referring to each other for some information, without support from external sources. In other words: circularity might make it difficult to uncover de facto original research.

Stabilising and improving Wikipedia's content by verification or attribution is done by basing Wikipedia's content on reliable and published external sources, not by basing it on other content in Wikipedia. Even if at some point in the future Wikipedia would be 99,99% error-free, self-referential sourcing should still be avoided in order to avoid that 0,01% errors would be multiplied into systemic errors. This doesn't mean that content can't be copied from one article to another. However, for any content on a page in main namespace (including transcluded content visible on that page) the verifiability of that content depends on the external sources indicated on that same page. Using external sources is instrumental in the avoidance of systemic errors. Or at least the systemic error won't be Wikipedia's but the external source's.

This also doesn't mean that the content of one Wikipedia article shouldn't be compared to the content of another article. On the contrary: avoiding POV forks by syncronising the content of articles (see for instance the sync template) or by merging the content of articles is also a way to improve the encyclopedia. The point is that for each individual page, whether syncronised or merged or whatever, compliance to Verifiability or Attribution can only be achieved by the external sources presented on that page.

An overview:
 * Wikilinks and Interwiki links effectuated with double square brackets, and visible in main namespace, play no role in the verification or attribution process for Main namespace content.
 * In main namespace, links to content of Wikimedia projects in external link format should generally be avoided (use Wikilinks or Interwiki links instead) and thus also play no role in the verification/attribution process. The only exception to that is data retrieved from accredited Wikimedia research projects in articles on covered Wikimedia projects. And even there such internal information should be used sparingly, but it is, for instance, allowed to use certain statistical data about Wikipedia in the article about Wikipedia, insofar as such data are covered by the Wikidemia project. But that's an exception, not the rule: if external data (for instance Alexa's) can be used that is largely preferred.
 * When copying, moving or translating content from whatever wiki page governed by the Wikimedia Foundation to whatever other page with content appearing in Wikipedia's main namespace, a copyrights-related attribution of the source needs to be given in the edit summary (see for instance Summary style). If the edit history of the source page is obliterated (which usually happens in a transwiki process), at least a number of principal authors need to be mentioned on the talk page of the target article (see for instance m:Help:Transwiki). Such attributions in edit history or on the talk page are no main namespace content and play no role for the compliance to Wikipedia's core content policies. Such attributions only relate to copyright obligations and the application of the Gnu Free Documentation License. The compliance to Verifiability or Attribution can, depending on case, be achieved by copying, moving or translating references together with the content, or by providing references to more appropriate or additional sources supporting the content on the target page.
 * Avoid circular sourcing via external sources. An external source may be based on the content of a Mediawiki project. Such "recycled" content has no value in a verification logic. For example, a publication discussing Wikipedia only has value as a source for Wikipedia's encyclopedia entry on Wikipedia for that part of the content of that external publication that is not a repeat of what can be found in Wikipedia itself.

Other namespaces
Other namespaces follow the same rules regarding avoidance of relying on internal sources as main namespace, apart from these exceptions:
 * Content visible in category namespace: usually, items listed in a category take their references (that is, external sources that justify the inclusion in the category) from Main namespace. So the reference is external, but accessed via Main namespace, not directly from Category namespace.
 * Image namespace: the author and/or copyright holder of an image may be a Wikipedian: in image namespace that is usually indicated by a link to User namespace. Some Image namespace content is sourced to a page with the same name at Wikimedia Commons.
 * Talk, Project, Help and User namespaces: in these namespaces there are legion verification links. For example if an article was listed for deletion, and the decision was "keep", a link to the page with that deletion discussion will be displayed on the talk page of the kept article.
 * Template namespace and transcluded content: Generally, verification is operated according to the verification rules of the namespace where the transcluded content is displayed. For instance, the featured template (intended for use on pages in talk namespace) contains a link to a page in Project namespace where it can be verified that the related article was indeed a featured article. A limited exception to the rule that the namespace where the transcluded content is displayed defines the rules is contained in Avoid self-references: some templates may contain internal links that play a temporary role in verification, in namespaces where this usually would not be allowed (for instance, a link from main namespace to a related talk page from the disputed template can be used to "verify" whether there is indeed an ongoing dispute over the article's content: when there is none, or the dispute has been resolved, the template should be removed from that page in Main namespace).
 * Media, Special and MediaWiki namespaces: have a completely different ruleset: they are highly self-referential (e.g. Special:DoubleRedirects is nothing but links to internal content) and rarely contain external references (Some do: e.g. MediaWiki:Sorbsreason contains a reference to http://www.sorbs.net).