Ranney, Austin
Harcourt, Brace and Company, 1956
Buku Teks
Laski, Harold J.
George Allen and Unwin, 1949
Buku Teks
McConnell, Grant
Alfred A. Knopf, 1967
Buku Teks
by William Ebenstein [and others]
Harper & Row, Publishers, 1970
Buku Teks
Irish, Marian D.
Prentice-Hall, 1962
Buku Teks