Alfred Jules Ayer
Alfred Jules Ayer (aka. A. J. Ayer and Freddie) (29 October 1910–1989) was a British philosopher best known for his statement of logical positivism and the verification principle in Language, Truth and Logic. In addition, he wrote about epistemology, especially questions of perception where he endorsed an account using sense-data, and the philosophy of David Hume. Ayer was Grote Professor of Mind and Logic at the University of London from 1946 to 1959 and the Wykeham Professor of Logic at the University of Oxford from 1959 to 1978.
The main thesis of Language, Truth and Logic is that a proposition, to be genuine or useful, must either be verifiable empirically or it is a tautology.