Grime, J.P.
John Wiley & Sons, 1979
Buku Teks
Trudgill, Stephen T.
Clarendon Press, 1979
Buku Teks
Moss, C.E. (Charles Edward)
Cambridge University Press, 2014
Buku Teks
Wojciechowski, Jerzy A.
Council for research in values and philosophy, [Date of publication not identified]
Buku Teks SO
Odum, Eugene Pleasants
Saunders College, 1983
Buku Teks