Incorporating significant editorial changes from earlier editions, the fourth edition of Ludwig Wittgenstein's Philosophical Investigations is the definitive en face German-English version of the most important work of 20th-century philosophy: The extensively revised English translation incorporates many hundreds of changes to Anscombe's original translation; Footnoted remarks in the earlier editions have now been relocated in the text; What was previously referred to as 'Part 2' is now republished as Philosophy of Psychology - A Fragment, and all the remarks in it are numbered for ease of reference; New detailed editorial endnotes explain decisions of translators and identify references and allusions in Wittgenstein's original text; Now features new essays on the history of the Philosophical Investigations, and the problems of translating Wittgenstein's text.