Leon Dyczewski, editor
Council for research in values and philosophy, 2002
Buku Teks
Michalak-Gray, Joanna, author
Teach Yourself , 2014
Buku Teks
edited by Mihaela Czobor-Lupp and J. Stefan Lupp
Council for Research in Values and Philosophy, 2002
Buku Teks
Univ of Hawai Press, 1986
Buku Teks
Pergamon Press, 1968
Buku Referensi