Early versus late Wittgenstein. Everyone changes their mind, but when you’re a philosopher with the depth of Ludwig Josef Johann Wittgenstein, you can express two positions and have others take great interest in both! Wittgenstein’s Tractatus Logico-philosophicus [Wittgenstein, 1922] was published in 1922 and is a primary reference for what we now think of as “early Wittgenstein”; Philosophical Investigations [Wittgenstein, 1953] was published in 1953 and characterizes the “late Wittgenstein.” In the interim, Wittgenstein taught elementary school, played music, and quit philosophy more than once. But even more striking than the passage of time between these two great works is how diametrically opposed the arguments put forward in Tractatus and Investigations are. N. Malcolm [Malcolm, 1967] expresses just how unusual a state of affairs this is:
A considerable part of the Investigations is an attack, either implicit or explicit, 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. [Malcolm, 1967, p. 334]
(Terry Winograd’s turnaround concerning appropriate applications of natural language processing (NLP) technology, between his dissertation and 1983 [Winograd, 1983] and his 1986 book with Flores [Winograd and Flores, 1986] almost qualifies for early-Winograd versus late-Winograd, however!:)

You can imagine my reluctance to attempt to characterize just what it was that Wittgenstein changed his mind about, in a short sidebar! Quite roughly then, early Wittgenstein thought that language was the perfect philosopher’s tool. He aspired to a universal language, shared by all careful users, that could positively and uniquely allow careful naming of things. Just as numbers point to essential categories and mathematics builds these into theorems about how numbers are related, simple words name simple categories of objects (events, states, ...), and more complicated linguistic expressions name more complicated categories, an utterance of language means the same thing wherever and whenever it is said, just as 2 does, and just as a2 + b2 = c2 remains true wherever.

By the time of his Investigations, Wittgenstein had given up hope that the convenient naming system of mathematics was possible elsewhere. Language for the late Wittgenstein depended critically on the context of the utterance. Naming things was only one possible language game; there are many others people play all the time. Without understanding the purposes to which an utterance is being applied, we can’t really understand its meaning. The meaning of a sentence is its use (Gebrauch), its employment (Verwendung), its application (Anwedung) [Malcolm, 1967, p. 336].

This book proceeds on the assumption that Wittgenstein got it right the second time; I focus especially on language serving the FOA language game. Your mileage may vary.