Williamson has contributed to
analytic philosophy of language,
logic,
metaphysics,
epistemology,
metaethics and
metaphilosophy. On
vagueness, he holds a position known as
epistemicism, which states that every seemingly vague
predicate (like "bald" or "thin") actually has a sharp cutoff, which is impossible for us to know. For instance, there is some number of hairs such that anyone with that number is bald, and anyone with even one more hair is not. In actuality, this condition will be spelled out only partly in terms of numbers of hairs, but whatever measures are relevant will have some sharp cutoff. This solution to the difficult
Sorites paradox was considered a surprising and unacceptable consequence, but has become a relatively mainstream view since his defence of it. Williamson is fond of using the statement, "no one knows whether I am thin" to illustrate his view. In
epistemology, Williamson suggests that
knowledge is unanalysable. This went against the common trend in philosophical literature up to that point, which was to argue that knowledge could be analysed into constituent concepts. (Typically, this would be
justified true belief plus an extra factor.) He agrees that knowledge entails justification, truth and
belief, but argues that it is conceptually primitive. He accounts for the importance of belief by discussing its connections with knowledge, but avoids the disjunctivist position of saying that belief can be analysed as the disjunction of knowledge with some distinct, non-
factive mental state. Williamson also argues against the traditional distinction of
knowing-how and
knowing-that. He claims that knowledge-how is a type of knowledge-that. Williamson argues that knowledge-how does not relate one's ability. He provides the example of a ski instructor who knows how to perform a complex move without having the ability to do it himself. In
metaphysics, Williamson defends necessitism, according to which necessarily everything is necessarily something; in short, that everything exists of necessity. Likewise, it is possible for something to have a property only if there is something which has that property. For instance, since it is possible for
Wittgenstein to have had a child, there is something which is a possible child of Wittgenstein. Necessitism is a theoretical interpretation of the
Barcan formula, which is a theorem of the
modal logic S5. However, Williamson has also developed an ontology of “bare possibilia” which he argues accounts for the seemingly unintuitive consequences of necessitism. == Publications ==