The article begins with the observation that Ockham was born in Yorkshire and not, as most standard reference works suppose, in the village of Ockham in Surrey. This curiosity was inserted by an IP address on 3 May 2010. The philosopher C. Delisle Burns proposed this in 1916, but I can find no modern reference work that says this. Some sources say that he actually came from Woking, which had a similar spelling in medieval times, but Wikipedia does not mention this at all.
When we turn to the work of a great person, it is much more difficult, because this requires understanding the work, and making a judgment about which parts of the work to emphasis and explain. This is particularly important with medieval philosophers because, mostly, we have very little information about their lives. We have an intimate and deep knowledge of what they thought, because we have their work. But this requires understanding their work, and so we turn to the work of Ockham according to Wikipedia.
The odd section on his philosophical thought begins "In scholasticism, Okham advocated a reform both in method and in content, the aim of which was simplification" which is straightforwardly lifted out of the Catholic Encyclopedia, and which illustrates an important principle of Wikipedia (and much of the Internet) that essays about more serious subjects (i.e. subjects unconnected with Pokemon, Star Trek episodes and 'porn star' biographies) are taken from out of copyright sources like the Catholic Encyclopedia, or the 1911 Britannica. The irony that an ultra modern high-tech medium like the Internet, when it reflects anything of importance, reflects the sometimes obselete views of 19th century scholars.
The section on nominalism is mostly lifted from the Catholic Encyclopedia, except for the paragraph at the end, where the abrupt change in style signals an entirely plagiarised excerpt from the Stanford Encyclopedia of Philosophy. The strange claim that Ockham has been called a "terminist", to distinguish him from a nominalist or a conceptualist, is from the Catholic Encyclopedia. Thus the article combines what is probably wrong ('terminism' can be consistent with nominalism**) with the section from the SEP which is intended for an academic audience, and is impenetrable out of context.
The whole section on Natural Philosophy is eccentric and strange, with a convoluted discussion of impetus theory, of the views of Mach and Whitehead, and of "the president of the Birmingham Scientific Society, George Gore". This section was added on 7 June 2007 by an editor who was later banned for promoting strange and eccentric views on the history of science. You can read the discussion here. It illustrates an important principle of Wikipedia, namely that many editors are like this, and eventually end up banned. Their reason for editing Wikipedia is to promote some pet theory that they could not get published in an academic journal, but will always be accepted by 'the encyclopedia that anyone can edit'.
The next section also mixes up passages from the Catholic Encyclopedia and the SEP, in a way that is highly misleading. It says that 'Ockham's Razor' is formulated by him as “For nothing ought to be posited without a reason given, unless it is self-evident (literally, known through itself) or known by experience or proved by the authority of Sacred Scripture.” The sentence is lifted verbatim from the SEP, except the SEP does not claim it is a formulation of the principle. Rather it suggests it is a sort of exception to the principle.
The original version of the article also copied the SEP claim that Ockham does not accept the Principle of Sufficient Reason. In a strange edit here made in 2006, an editor changes this to 'accepts' the principle. This is the same editor who added the plagiarised sections from the Catholic Encyclopedia, and whose contribution history suggests many such insertions, including a whole article about the late Scholastic philosopher Zabarella. Note that Wikipedia now contradicts itself, for the article on Ockham's Razor still retains the claim that Ockham did not accept the Principle of Sufficient Reason.
Theory of knowledge
The section on Ockham's theory of knowledge is clearly not plagiarised; the style is too amateurish and clumsy. As Dr Johnson once quipped: "Your work is both good and original. Unfortunately the parts which are good are not original, and the parts which are original are not good". (Or something like that).
The section on his political is reasonably written and seems reasonably accurate (although I am not an expert on this aspect of Ockham). It is however very brief, given the importance which experts attach to his work. if he really was one of the first medieval authors to advocate a form of separation between church and state, why does Wikipedia devote far less space (one sentence) than it does to the biography of a porn star?
The section on Ockham's logic is also remarkable for its brevity, considering that Ockham's fame rests mostly on his logical work, the magisterial and compendious Summa Logicae. It mentions only Ockham's anticipation of De Morgan's laws, and of many-valued logic. The latter claim is completely misleading. It illustrates the tendency of all reference work to emphasise the ideas of thinkers which anticipate, or seem to anticipate, later developments in philosophy and science, at the expense of other interesting ideas they may have had. No source is given; it probably comes from Ockham's defence of the 'traditional' interpretation of Aristotle (in Exposition in Librum Perihermenias I.6.15 - see the SEP article here). But it fails to mention that nearly all commentators on the famous 'sea battle' problem discussed by Aristotle were exercised by the problem of statements about future events, and by the possibility that such statements are neither true nor false. Thus the idea of a third 'truth value' did not originate with Ockham, and may have originated with Aristotle, depending on how you interpret Aristotle.
In summary: the Wikipedia article on William of Ockham, one of England's most illustrious and important philosophers, is woefully incomplete and inaccurate. It mixes blatant plagiarism with blatant falsehood. This is not surprising. What is surprising is the way that the respectable press eulogises Wikipedia, respectable institutions like the British Museum are entering into partnership with it, respectable donors like the Sloan Foundation are contributing large sums of money to it. This needs to change, although it is hard to see how.
* Permalink: version of 24 June 2010.
** Particularly in the case of Ockham's nominalism, defined as the view that we should not multiply entities according to the multiplicity of names.