Burickson, Sherwin
Philosophical Library, 1959
Buku Referensi
Keylor, William R., 1944-
Oxford University Press, 1996
Buku Teks
Grenville, J.A.S.
Routledge, 2005
Buku Teks
Palmer, Alan
Penguin Books , 1987
Buku Referensi
Shuter, Paul
Heineman Educational , 1988
Buku Teks