Handlin, Oscar, author
Atheneum, 1966
Buku Teks
Mill, John Stuart, author
David Campbell Publisher, 1992
Buku Referensi
Walker, Patrick Gordon, author
Hutchinson & Company, 1951
Buku Teks
Laski, Harold J., author
George Allen and Unwin, 1948
Buku Teks
Pallister, Anne, author
Oxford University Press, 1972
Buku Teks