Jones, Stephanie
Prentice-Hall, 1995
Buku Teks
edited by Gary Fuller, Robert Stecker, and John P. Wright.
Routledge, 2000
Buku Referensi
Hanke, John E.
Richard D. Irwin, 1994
Buku Teks SO
Locke, John
J.M. Dent & Sons, 1947
Buku Teks SO
Locke, John
Hackett Publishing Company, Inc., 1996
Buku Teks SO