"One of the most impressive pieces of scholarship I have ever encountered."-W. E. Kennick, Amherst College There is nothing in the literature on the Philosophical Investigations comparable to this learned and exhaustive commentary. Offering both information and interpretation, it is a remarkable book that fills a recognized need for a close study of one of the world's major works of philosophy. After a general introduction, Father Hallett divides the text of the Investigations into forty-one units, and then provides an introduction to each section, along with detailed comments on individual paragraphs, statements, and expressions. His use of paragraph numbers in the general introduction and in the sectional introductions permits ready reference downward, for detailed development or illustration of a general observation, or upward, from a particular passage to its wider context. To clarify the philosophical point of Wittgenstein's remarks, Father Hallett makes frequent references to other parts of the Investigations; to Wittgenstein's other writings, both published and unpublished; and to the works which Wittgenstein knew and often had in mind, such as those of Frege, Russell, Moore, James, Augustine, Plato, Schlick, and Kohler. Father Hallett also cites and quotes secondary sources, and he includes an appendix relating Wittgenstein to more than 150 authors, particularly those of his own generation or earlier whom he read, or knew personally, and who are mentioned in this commentary. Written in straightforward and lucid prose, this outstanding book reveals continuities in Wittgenstein's thought over long periods of time. It is an indispensable guide for those preparing courses on the Investigations and a useful tool for students taking those courses.