Hundert, Edward M.
Harvard University Press , 1995
Buku Teks
Pinker, Steven
Penguin Books, 2002
Buku Teks
edited by Robert M. Losee
Springer-Verlag, 2012
eBooks
Graham, Frank D.
Princeton University press, 1948
Buku Teks
Wojciechowski, Jerzy A., author
Council for research in values and philosophy, [Date of publication not identified]
Buku Teks SO