Wicksell, Knut
George Routledge and Sons , 1946
Buku Teks
Paolo Janni
The council for research in values and philoaophy, 2001
Buku Teks
Schiller, Bradley R.
Prentice-Hall, 1975
Buku Teks
Brown, A.J.
George Allen and Unwin, 1959
Buku Teks
Robinson, Marshall A.
Brookings Institution, 1955
Buku Teks