Philosophical Investigations (Philosophische Untersuchungen) 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.He alleges that the problems are traceable to a set of related assumptions about the nature of language, which themselves presuppose a particular conception of the essence of language. This conception is considered and ultimately rejected for being too general; that is, as an essentialist account of the nature of language it is simply too narrow to be able to account for the variety of things we do with language. Wittgenstein begins the book with a quotation from St. Augustine, whom he cites as a proponent of the generalized and limited conception that he then summarizes:The individual words in language name objects—sentences are combinations of such names. In this picture of language we find the roots of the following idea: Every word has a meaning. This meaning is correlated with the word. It is the object for which the word stands.He then sets out throughout the rest of the book to demonstrate the limitations of this conception, including, he argues, with many traditional philosophical puzzles and confusions that arise as a result of this limited picture. Within the Analytic tradition, the book is considered by many as being one of the most important philosophical works of the 20th century, and it continues to influence contemporary philosophers, especially those studying mind and language.