Cita APA (7a ed.)

Ridley, M. (1997). The origins of virtue. Penguin.

Cita Chicago Style (17a ed.)

Ridley, Matt. The Origins of Virtue. London [etc.]: Penguin, 1997.

Cita MLA (9a ed.)

Ridley, Matt. The Origins of Virtue. Penguin, 1997.