Arblaster, Anthony
Open University Press, 1987
Buku Teks
Schulz, Ernest B
[publisher not identified], 1956
Buku Teks
Mackie, Gerry
Cambridge University Press, 2003
Buku Teks SO
Eisenstadt, Shmuel Noah
The Woodrow Lilson Center Press, 1999
Buku Teks
Lindsay, A.D.
Oxford University Press, 1948
Buku Teks SO