<b>G.P.Baker</b> was a Fellow of St John’s College, Oxford from 1967 until his death in 2002. He is the co-author with P.M.S. Hacker of the first two volumes of the four-volume <i>Analytical Commentary on the Philosophical Investigations</i> (Blackwell, 1980–96), author of <i>Wittgenstein, Frege and the Vienna Circle</i> (Blackwell, 1988) and with Katherine Morris of <i>Descartes’ Dualism</i> (1996). He also wrote numerous articles on Wittgenstein, Frege, Russell, Waismann and Descartes. <p><b>P.M.S. Hacker</b> is the leading authority on the philosophy of Wittgenstein. He is author of the four-volume <i>Analytical Commentary on the Philosophical Investigations</i>, the first two volumes co-authored with G.P. Baker (Blackwell, 1980–96) and of <i>Wittgenstein’s Place in Twentieth-century Analytic Philosophy</i> (Blackwell, 1996). His other previous works include <i>The Philosophical Foundations of Neuroscience</i> (Blackwell, 2003) and <i>History of Cognitive Neuroscience</i> (Wiley-Blackwell, 2008), both co-authored with M.R. Bennett. Most recently he has published <i>Human Nature: The Categorical Framework</i> (Blackwell, 2007), the first volume of a trilogy on human nature.Together with Joachim Schulte, he has produced the 4<sup>th</sup> edition and extensively revised translation of Wittgenstein’s <i>Philosophical Investigations</i> (Wiley-Blackwell, forthcoming 2009).</p>