Palmer, Alan
Penguin Books, 1981
Buku Referensi
Palmer, Alan
Penguin Books , 1987
Buku Referensi
Burickson, Sherwin
Philosophical Library, 1959
Buku Referensi
edited by G. Goodwin
Cambridge University Press, 1958
Buku Teks
Palmer, Robert Roswell, 1909-2002
McGraw-Hill, 1992
Buku Teks