Blue and Brown Books

The Blue and Brown Books are two sets of notes taken during lectures conducted by Ludwig Wittgenstein from 1933 to 1935. They were mimeographed as two separate books, and a few copies were circulated in a restricted circle during Wittgenstein's lifetime. The lecture notes from 1933–1934 were bound in blue cloth, and the notes dictated in 1934–1935 were bound in brown. Rush Rhees published these 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 these offer textual evidence for the genesis of what became known as Wittgenstein's later philosophy.