After completion of the first part of his Philosophical Investigations Wittgensteins's discussions in his post-war manuscripts up to 1949 chiefly concern the nature of certain psychological concepts. These manuscripts, not the selections from them published so far, are here used as a basis for reconstructing the central arguments and conceptual elucidations developed by Wittgenstein that period. There is a certain continuity in Wittgenstein's thought which shows itself in his considerations of foundational problems and in his reflections on language games. What comes as a surprise, however, are his various attempts at "systematic" analyses of psychological concepts and his very detailed criticism of Köhler's Gestalt psychological notion of visual object. One of the central subjects of Wittgenstein's later thought is the connection between instinctive reactions, linguistic and non-linguistic context, and mastery of a technique. This connection is explored by way of clarifying the concepts "experience", "sensation", "understanding", and the results of this clarification are illuminating contributions to aesthetics and the theory of meaning. Wittgenstein's thoughts on the logic of language reflections on psychological concepts are closely knit. This is shown by his discussion of Moore's paradox, which sheds new light both on the limits of logical analysis and on certain curious features of the concepts "believe", "assume", "assert". At the same time this is his last sustained treatment of a number of Fregean ideas which had been the object of fruitful criticisms by Wittgenstein since the time of his very first writings. Of interest to: Philosophers, logicians, linguistics, psychologists