Pojman, Louis P.
Thomson Wadsworth, 2006
Buku Teks
Fieser, James
Oxford University Press, 2005
Buku Teks
edited by Ralph E. Pumphrey and Muriel W. Pumphrey
Columbia University Press, 1961
Buku Teks
Stumpf, Samuel Enoch, 1918-1998
McGraw-Hill, 1971
Buku Teks
UNESCO , 1977
Buku Teks