Modden, David
New York, Twayne, 1964
Buku Teks
Huber, Carlo
The Council for Research Values and Philosophy , 2001
Buku Teks
Lari, Sayyid Mujtaba Musavi
Foundation of Islamic Cultural Propagation in The World, 1993
Buku Teks
White, David Manning
Macmillan, 1983
Buku Teks
Siegel, James T., 1937-
University of California Press, 1969
Buku Teks