THe Free Press, 1961
Buku Teks
Pojman, Louis P., author
McGraw-Hill , 2003
Buku Teks
Corbett, Sister Thomas Albert
University of America Press, 1950
Buku Teks
Schumaker, Paul, author
Blackwell Publishing, 2008
Buku Teks
edited by Carl J. Friedrich
The Modern Library, 1949
Buku Teks