APA (7th ed.) Citation

Paulsen, F., & Thilly, F. (1899). A system of ethics. C. Scribner's Sons.

Chicago Style (17th ed.) Citation

Paulsen, Friedrich, and Frank Thilly. A System of Ethics. New York: C. Scribner's Sons, 1899.

MLA (9th ed.) Citation

Paulsen, Friedrich, and Frank Thilly. A System of Ethics. C. Scribner's Sons, 1899.