In Philosophical Investigations, Ludwig Wittgenstein presents a radical approach to the philosophy of language and the mind, setting out a startlingly fresh conception of philosophy itself. Wittgenstein begins from the insight that most philosophical problems trace back to incorrect assumptions about the nature of language. While previous works typically described a problem and debated solutions, Wittgenstein takes the unique approach of treating philosophy not as a theory, but as an activity. He urges philosophers to concern themselves with ordinary life. Investigations revolutionized English-language philosophy and is consistently cited as one of the most influential works of the century.