First edition. ‘Wittgenstein refrained from publishing the Investigations during his lifetime, but his explicit wish was that it be published posthumously, a wish that he probably did not have with respect to any of the rest of the voluminous work he produced between 1929 and 1951. … Wittgenstein believed that the Investigations could be better understood if one saw it against the background of [his 1922 book, the] Tractatus. A considerable part of the Investigations is an attack, either explicit or implicit, on the earlier work. This development is probably unique in the history of philosophy — a thinker producing, at different periods of his life, two highly original systems of thought, each system the result of many years of intensive labors, each expressed in an elegant and powerful style, each greatly influencing contemporary philosophy, and the second being a criticism and rejection of the first’ (Norman Malcolm in The Encyclopedia of Philosophy).