Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Sir Alfred Jules Ayer, better known as A. J. Ayer or "Freddie" to friends, was a British philosopher known for his promotion of logical positivism, particularly in his books Language, Truth and Logic and The Problem of Knowledge. Ayer was the Grote Professor of the Philosophy of Mind and Logic at University College London from 1946 until 1959, when he became Wykeham Professor of Logic at the University of Oxford. He was president of the Aristotelian Society from 1951 to 1952. He was knighted in 1970.