Ruse, Michael
Cambridge University Press, 2012
Buku Teks
Keith, Arthur, Sir
Watts & Co., 1950
Buku Teks
Keith, Arthur Berriedale, 1879-1944
Watts & Co., 1947
Buku Teks
Barnard, Alan
Cambridge University Press, 2011
Buku Teks
Kraus, Bertram S.
Harper & Row, 1964
Buku Teks