P. M. S. Hacker is a fellow of St John's College, Oxford. He is author of numerous books and articles on philosophy of mind and philosophy of language, and a leading authority on the philosophy of Wittgenstein. Among his many publications on Wittgenstein is the monumental four volume Analytical Commentary on the Philosophical Investigations published by Blackwell, the first two volumes of which are co-authored with G. P. Baker.