Philosophical Investigations is a highly influential work by the 20th-century philosopher Ludwig Wittgenstein. In it, Wittgenstein discusses numerous problems and puzzles in the fields of semantics, logic, philosophy of mathematics, philosophy of psychology, philosophy of action, and the philosophy of mind. He puts forth the view that conceptual confusions surrounding language use are at the root of most philosophical problems, contradicting or discarding much of what he argued in his earlier work, the Tractatus Logico-Philosophicus.