Alfred Jules Ayer (October 29, 1910 - June 27, 1989), better known as simply A. J. Ayer (and called Freddie by friends), was a British philosopher. He helped to popularise logical positivism in English-speaking countries in his books Language, Truth and Logic (1936) and The Problem of Knowledge (1956).

He was educated at Eton College, and served in the British military during World War II. In some ways he was the philosophical successor to Bertrand Russell, although he gained fame more for adapting ideas of others than for true originality.

He is perhaps best known for his verification principle, an attempt at creating a process for determining whether a sentence has any logical meaning. At several periods he taught or lectured in the United States, including serving as a visiting professor at Bard College in the fall of 1987, when he taught classes on "Moore and Russell" and "Ryle and Austin."

Shortly before his death in 1989 he received publicity after having an unusual near-death experience, which to some suggested that he had moved away from his lifelong and famous religious skepticism . He may however simply have been attempting to report his experiences, in an honestly objective, empirical manner.

At a party Ayer, then 77, encountered Mike Tyson harassing Naomi Campbell and demanded Tyson stop. Tyson said "Do you know who the fuck I am? I'm the heavyweight champion of the world." Ayer replied "And I am the former Wykeham Professor of Logic . We are both pre-eminent in our field; I suggest that we talk about this like rational men."

See also: a priori knowledge

Further reading

• Ben Rogers, A.J. Ayer: A Life, Grove Press, 2001.