Das Blaue Buch. Eine Philosophische Betrachtung. (Das Braune Buch).

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The Blue and Brown Books are two sets of notes taken during lectures conducted by Ludwig Wittgenstein between 1933 and 1935. They were mimeographed as two separated books and a few copies were circulated in a restricted circle during Wittgenstein's lifetime. The lecture notes from 1933–4 were bound in blue cloth and the notes dictated in 1934–5 were bound in brown. Rush Rhees published them together for the first time in 1958 as Preliminary Studies for the "Philosophical Investigations".
Inchoate versions of many of the ideas that would later be more fully explored in the Philosophical Investigations are found there, so they offer textual evidence for the genesis of what became known as Wittgenstein's later philosophy.