Commons, John R.
Macmillan, 1934
Buku Teks
Daugherty, Carroll R.
Houghton Miffiln, 1950
Buku Teks
Wicksteed, Philip Henry, 1844-1927, author
Augus M. Kelley, 1950
Buku Teks
Mill, John Stuart
Colonial Press, 1898
Buku Klasik
Mussey, Henry R.
Ginn and Company, 1947
Buku Teks