Philosophical Investigations (1953), published after Austrian philosopher Ludwig Wittgenstein's death, is nothing short of a complete redefinition of philosophy and language. In addition to being a reimagining of philosophy as a discipline as well as language, Philosophical Investigations is in strict counterpart to his earlier work Tractatus Logico Philosophicus (1922). For this reason Philosophical Investigations is best read alongside or with reference to Tractatus. In the latter, Wittgenstein contends that language has a basis in reality. Complex sentences can be broken down into simple ones. Also according to Tractatus, the world is composed of facts.

In Philosophical Investigations, Wittgenstein turns this on his head. He says that language is more fluid and has no representational meaning but a fluid meaning that is generated through use. Wittgenstein gives an example of a "five red apples" in which case the designation of "five" is proof of the fact that language is not representational, but its meaning is derived from use. In generating this definition of language, Wittgenstein rejects the Augustinian definition of language as "ostensive" (a mechanism whereby one learns the meaning of words by being show representation of the objects these words represent).

Philosophical Investigations is also expert in its use of metaphors. For example, he claims that language operates in "language-games" which, according to Wittgenstein is represented by everything from reporting an event to making a request to making a joke. Language is given meaning from its use, and the use itself is evidence of activity, which in turn must evidence a form of life that is engaging in the activity. This is a huge philosophical contention (that language evidences a form of life).

Another metaphor is that the meanings within a word's semantic range resemble one another in the same way that members of a family do; there are no strict resemblances necessarily required, but an overall resembles owing to select similarities.

Wittgensteins' Philosophical Investigations is one of the most seminal pieces of linguistic philosophy from an unorthodox philosopher who, since his death, has been regarded as a genius in the field.