Külpe, O., Pillsbury, W. B., & Titchener, E. B. (1901). Introduction to philosophy: A handbook for students of psychology, logic, ethics, æsthetics and general philosophy. S. Sonnenschein & co., limited; The Macmillan Co..

Külpe, Oswald, W. B. Pillsbury, and Edward Bradford Titchener. Introduction to Philosophy: A Handbook for Students of Psychology, Logic, Ethics, æsthetics and General Philosophy. London, New York: S. Sonnenschein & co., limited; The Macmillan Co., 1901.

Külpe, Oswald, et al. Introduction to Philosophy: A Handbook for Students of Psychology, Logic, Ethics, æsthetics and General Philosophy. S. Sonnenschein & co., limited; The Macmillan Co., 1901.