Reflections on Knowledge and its Limits∗

Williamson’s Knowledge and its Limits is the most important philosophical discussion of knowledge in many years. It sets the agenda for epistemology for the next decade and beyond. The main thesis of the book is “knowledge first.” One aspect of this thesis is that knowledge is a basic mental state, a propositional attitude that cannot be explained in terms of belief plus certain other conditions. Given that knowledge counts as a mental state, it follows that people who are internal physical duplicates can be in different mental states. Since a person in a “good” normal situation of veridical perception knows things that are not known by a person who is internally a duplicate but externally ∗Timothy Williamson, Knowledge and its Limits, (Oxford: Oxford University Press, 2000), pp. xi, 340. †I am indebted to Elizabeth Harman and Mark Greenberg for very useful extensive comments on earlier drafts.