It is difficult to over-estimate the extent to which Russell's thought dominated twentieth century analytic philosophy: virtually every strand in its development either originated with him or was transformed by being transmitted through him. Analytic philosophy itself owes its existence more to Russell than to any other philosopher. He was not, of course, its only originator (Frege and Moore, must be acknowledged as well), but he contributed more across its central areas (logic, philosophy of language, epistemology, and metaphysics) than any other single philosopher, and he was certainly its most energetic propagandist. Moreover, as Pigden forcefully argues in his essay in this volume, even in areas such as ethics, where Russell's work has often been thought to be shallow and derivative, Russell has been the source of a number of innovations which might have made the reputation of a lesser philosopher. With Frege and Peano, Russell created modern formal logic and, much more than they, was responsible for bringing it to the attention of philosophers and demonstrating its usefulness in philosophical applications. His work had a profound influence on Carnap and the logical positivists, on Quine, on A.J. Ayer, and in diverse ways on Wittgenstein. Wittgenstein's Tractatus Logico-Philosophicus [1922] was an attempt (ultimately unsustainable) to push to the limit an approach to language which had been suggested, though not actually embraced, by Russell. Wittgenstein's later philosophy was an attempt to make good the defects of the Tractatus by pushing equally far in the opposite direction. The ordinary language philosophers of the middle of the century also reacted strongly against Russell; by the same token, their work would have been inconceivable without him.