 The comparatively unusual nature of the second part is due to the fact that it comprises notes that Wittgenstein may have intended to re-incorporate into the first part.After his death, the text was published as a "Part II" in the first, second and third editions.However, in light of continuing uncertainty about Wittgenstein's intentions regarding this material, the fourth edition (2009) re-titles "Part I" as "Philosophical Investigations" proper, and "Part II" as "Philosophy of Psychology – A Fragment."