Sir Alfred Jules "Freddie" Ayer FBA (/ɛər/; 29 October 1910 – 27 June 1989), usually cited as A. J. Ayer, was an English philosopher known for his promotion of logical positivism, particularly in his books Language, Truth, and Logic (1936) and The Problem of Knowledge (1956). He was educated at Eton College and the University of Oxford, after which he studied the philosophy of logical positivism at the University of Vienna. From 1933 to 1940 he lectured on philosophy at Christ Church, Oxford. During the Second World War Ayer was a Special Operations Executive and MI6 agent.