It is usually assumed that Wittgenstein's philosophical development is determined either by one dramatic or one subtle change of mind. This book challenges the one-change view. Wittgenstein had many changes of mind and they are so substantial that he can be understood as holding several different philosophies in the late twenties and early thirties. Early in 1929, Wittgenstein envisages a complementary (phenomenological) symbolism in order to carry out the Tractarian task of giving the limits of language and thought. The symbolism failed and he then developed a comprehensive notion of 'grammar' that, he hoped, would fulfill the task. This notion of 'grammar' leads in 1930-1 to the calculus conception of language, which is still defended in the Big Typescript (1932-3). As a complementary tool of the calculus conception, Wittgenstein invents the genetic method, which aims at dissolving philosophical puzzles by the understanding of how they come about. After the Big Typescript, Wittgenstein assimilates an anthropological perspective and puts the genetic method at the center of the stage of his philosophy. The use of the genetic method (associated with an anthropological perspective) develops gradually, taking various forms of application: in the Blue Book, in the versions of the Brown Book (1934-6), and in the Philosophical Investigations.

The book explains why and how Wittgenstein adapted the Tractatus in phenomenological and grammatical terms to meet challenges of his 'middle period.' It also shows why and how he invents a new method and develops an anthropological perspective, which gradually frame his philosophy and give birth to the Philosophical Investigations .