Gorman, Alfred H.
Allyn and Bacon, 1969
Buku Teks
Starr, Wilmarth H.
American Book Company, 1959
Buku Teks
Jensen, Alfred
McGraw-Hill Kogakusha, 1975
Buku Teks
Hausrath, Alfred H.
McGraw-Hill, 1971
Buku Teks
Dilthey, Wilhelm
The UNiversity of North Carolina Press, 1954
Buku Teks