British philosopher, responsible for introducing the principles of logical positivism of the Vienna Circle to British philosophers. He was knighted in 1970.
Born in London, Ayer was educated at Christ Church, Oxford, where he was a pupil of Gilbert Ryle. On Ryle's suggestion Ayer, after graduating in 1932, enrolled at the University of Vienna and attended the regular meetings of the Viennese positivists centred around Schlick. Ayer became converted to the exciting new doctrines vigorously argued by the logical positivists and consequently, on his return to Oxford (1933), he began to prepare an account of their work that eventually became Language, Truth, and Logic (1936), one of the most successful philosophical works of the century. In it Ayer followed the positivists in formulating the verification principle, with which he could demonstrate the meaninglessness of all metaphysics and theology, and the vacuousness of all ethical propositions. Such views did not impress many of Oxford's more traditional philosophers, who resisted for some time attempts to find a suitable academic appointment for Ayer in Oxford. Eventually he was appointed to the staff of his own college, Christ Church. After service with the Welsh Guards during World War II Ayer returned briefly to Oxford in 1945 before being appointed (in 1946) Grote Professor of the Philosophy of Mind and Logic at University College, London. He became Wykeham Professor of Logic at Oxford in 1959, a post he held until his retirement in 1977.
Although in his later work Ayer qualified many and rejected some of the claims made in his first book, he continued to adhere to the spirit if not the letter of the positivist programme laid down in the Vienna of the early 1930s. Working mainly in the field of epistemology, he tried to show in such works as The Foundations of Empirical Knowledge (1940) and The Problem of Knowledge (1956) how we could justifiably, on empiricist assumptions, come to know truths about such phenomena as the external world, other minds, and the past. These two works were supplemented by four collections of his philosophical essays published in 1954, 1963, 1969, and 1972.