Trilling, Lionel
Meridian Books, 1955
Buku Teks SO
Wicksell, Knut
George Routledge and Sons , 1946
Buku Teks SO
Triling, Lionel
The Vall0Ballou Press Inc., 1943
Buku Teks SO
Enos, Matthew
Wadsworth, 2002
Buku Teks SO
G.P. Putnam's Sons, 1958
Buku Teks SO