APA (7th ed.) Citation

Ayer, A. J. (1956). The problem of knowledge. Penguin.

Chicago Style (17th ed.) Citation

Ayer, A. J. The Problem of Knowledge. London ; Ringwood, Vic.: Penguin, 1956.

MLA (8th ed.) Citation

Ayer, A. J. The Problem of Knowledge. Penguin, 1956.