Morton, Adam, author
Blackwell, 1997
Buku Teks
O`Brien, Dan, author
Polity Press, 2006
Buku Teks
Lewis, Clarence Irving, author
Dover, 1956
Buku Teks
Chisholm, Roderick M., author
Prentice Hall International, 1989
Buku Teks
Rescher, Nicholas, author
State University of New York Press, 2003
Buku Teks