Benton, Ted
Palgrave Macmillan, 2011
Buku Teks
Ryan, Alan
Oxford , 1970
Buku Teks
Morkuniene, Jurate
Council for Research in Values and Philosophy, 2004
Buku Teks
edited by Richard Boyd, Philip Gasper, and J. D. Trout
Bradford Book, 1997
Buku Teks
Levison, Arnold B.
Pegasus, 1974
Buku Teks