The Blue and Brown Books are two sets of notes taken during lectures conducted by Ludwig Wittgenstein

Ludwig Wittgenstein

Ludwig Josef Johann Wittgenstein was an Austrian philosopher who worked primarily in logic, the philosophy of mathematics, the philosophy of mind, and the philosophy of language. He was professor in philosophy at the University of Cambridge from 1939 until 1947...

 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

Rush Rhees

Rush Rhees was a philosopher at Swansea University from 1940 to 1966Rhees is principally known as a student, friend, and literary executor of the philosopher Ludwig Wittgenstein. With G. E. M. Anscombe, he edited Wittgenstein's posthumous Philosophical Investigations , a highly influential work...

 published them together for the first time in 1958 as Preliminary Studies for the "Philosophical Investigations", Generally known as The Blue and Brown Books by Ludwig Wittgenstein.

Inchoate versions of many of the ideas that would later be more fully explored in the Philosophical Investigations

Philosophical Investigations

Philosophical Investigations is, along with the Tractatus Logico-Philosophicus, one of the most influential works by the 20th-century philosopher Ludwig Wittgenstein...

 are found there, so they offer textual evidence for the genesis of what became known as Wittgenstein's later philosophy.

The Blue Book

The Blue Book was dictated between 1933 and 1934, and contains certain themes unaddressed in Wittgenstein's later works, including deliberations on thinking as operating with signs. An early conception of what would later become known as language-games is present in the text, which represents the first period of Wittgenstein's thought after 1932, a method of linguistic analysis which would later become ordinary language philosophy

Ordinary language philosophy

Ordinary language philosophy is a philosophical school that approaches traditional philosophical problems as rooted in misunderstandings philosophers develop by distorting or forgetting what words actually mean in everyday use....

.

The Brown Book

During the academic year 1934-5 Wittgenstein dictated to Francis Skinner

Francis Skinner

Francis Skinner was a friend, collaborator, and alleged lover of the Austrian philosopher Ludwig Wittgenstein. He was born in 1912 in Letchworth, Hertfordshire, England. While studying mathematics at Cambridge in 1930, Skinner fell under Wittgenstein's influence and "became utterly, uncritically,...

 and Alice Ambrose

Alice Ambrose

Alice Ambrose Lazerowitz was an American philosopher, logician, and author.Alice Ambrose was born in Lexington, Illinois and studied philosophy and mathematics at Millikin University. After completing her PhD at the University of Wisconsin–Madison in 1932, she went to Cambridge University to study...

a text of which three copies were typed and bound. Later it became known as 'the Brown book'. Wittgenstein contemplated publishing and attempted a German revision, but ultimately abandoned the project as worthless.