Alfred Jules "Freddie" Ayer (29 October 1910 – 27 June 1989) was a British philosopher known for his promotion of logical positivism, particularly in his books Language, Truth, and Logic (1936) and The Problem of Knowledge (1956).
Ayer was a Special Operations Executive and MI6 agent during the Second World War. He 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.
Among British philosophers of the 20th century, he has been ranked by Stanford as second only to Bertrand Russell.