APA
Ruggiero G. d., . (1921). Modern philosophy. London: George Allen & Unwin.
Chicago
Ruggiero Guido de, . 1921. Modern philosophy. London: George Allen & Unwin.
Harvard
Ruggiero G. d., . (1921). Modern philosophy. London: George Allen & Unwin.
MLA
Ruggiero Guido de, . Modern philosophy. London: George Allen & Unwin. 1921.