Ludwig Wittgenstein was an Austrian-British philosopher who worked primarily in logic, the philosophy of mathematics, the philosophy of mind, and the philosophy of language.

1. Tractatus Logico-Philosophicus
2. Philosophical Investigations

The Picture Theory of Language, presented in the Tractatus, states that language functions as a picture or model of reality, and that the structure of language reflects the structure of the world.

Language-games, introduced in Philosophical Investigations, refer to simple examples of language use and the actions into which the language is woven. Wittgenstein used this concept to show that the meaning of words is derived from their use in various contexts.

The Private Language Argument, presented in Philosophical Investigations, contends that a language understandable by only a single individual is incoherent. Wittgenstein argues that for a language to be meaningful, it must be possible for others to understand it.

In his early work (Tractatus), Wittgenstein believed that philosophy should clarify the logical structure of language and thought. In his later work (Philosophical Investigations), he saw philosophy as a tool for clearing up conceptual confusions in everyday language use.

The "Beetle in a Box" thought experiment, from Philosophical Investigations, illustrates the problem of private sensations. It suggests that if everyone had a box with something called a "beetle" inside, but could only see their own beetle, the word "beetle" would come to mean "that thing in everyone's box," regardless of what was actually inside each box.