These works, as the subtitle makes clear, are unfinished sketches for Philosophical Investigations, among the most important & influential philosophical work of modern times. The 'Blue Book' is a set of notes dictated to Witgenstein's Cambridge students in 1933-34. The 'Brown Book' was a draft for what eventually became the growth of the first part of Philosophical Investigations. This book reveals the germination & growth of the ideas which found their final expression in Witgenstein's later work. It's indispensable therefore to students of Witgenstein's thought & to all those who wish to study at firsthand the mental processes of a thinker who fundamentally changed the course of modern philosophy.