Hirsch, Eric Donald, Jr.
Houghton Miffiln, 2002
Buku Referensi
Chapman, Robert L.
London Pan Books 1988
Buku Referensi
Reifer, Mary
Philosophical Library, 1955
Buku Referensi
Geddes & Grosset, 2000
Buku Referensi
edited by. Frank Gaynor
New York, Philosophical library, 1951
Buku Referensi