Greenwood Press, 1977
Buku Referensi
Barnes, Winston H. F., author
Adam & Charles Black, 1950
Buku Teks
Langer, Susanne K., author
John Hopkins Press, 1964
Buku Teks
Ziman, John, author
Cambridge University Press, 1994
Buku Teks
Tran, Van Doan, author
The council for research in values and philosophy, 2001
Buku Teks