Nussbaum, Arthur
Macmillan, 1958
Buku Teks
Younger, R. M.
Victoria Hutchinson Group 1982
Buku Teks
Goldschmidt, Arthur
Westview Press, 1983
Buku Teks
editor Thomas C. Cochran, Wayne Andrew
Charles Scribner's Sons , 1962
Buku Referensi
Burickson, Sherwin
Philosophical Library, 1959
Buku Referensi