Cita APA (7a ed.)

Santayana, G. (1923). The unknowable. The Herbert Spencer lecture. Delivered a Oxford, 24 october, 1923. At the Clarendon press.

Cita Chicago Style (17a ed.)

Santayana, George. The Unknowable. The Herbert Spencer Lecture. Delivered a Oxford, 24 October, 1923. Oxford: At the Clarendon press, 1923.

Cita MLA (8a ed.)

Santayana, George. The Unknowable. The Herbert Spencer Lecture. Delivered a Oxford, 24 October, 1923. At the Clarendon press, 1923.