[2] 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.
[1] The Blue Book was dictated from 1933 to 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.
While Wittgenstein in The Blue Book is not dogmatic nor systematic, he does provide arguments that point toward a more self-critical view of language.
He writes: If we are taught the meaning of the word 'yellow' by being given some sort of ostensive definition [in this case, ostensive means something like "denoting a way of defining by direct demonstration, e.g., by pointing"] (a rule of the usage of the word) this teaching can be looked at in two different ways: (a) The teaching is a drill.
[5] During the academic year 1934–1935, Wittgenstein dictated to Francis Skinner and Alice Ambrose a text of which three copies were typed and bound.
[8] In the novel A Philosophical Investigation by Phillip Kerr, a dialogue between a killer identified as neuro-anatomically different and an intuitive female detective occurs.
Eventually he is identified but attempts suicide prior to his anticipated trial and punishment by induction of permanent vegetative coma which has replaced the death penalty.