APA (7th ed.) Citation

Hughes, G. E., & Cresswell, M. J. (1968). An introduction to modal logic. Methuen.

Chicago Style (17th ed.) Citation

Hughes, George Edward, and M. J. Cresswell. An Introduction to Modal Logic. London: Methuen, 1968.

MLA (9th ed.) Citation

Hughes, George Edward, and M. J. Cresswell. An Introduction to Modal Logic. Methuen, 1968.