Keyes, Charles Don
Routledge, 1999
Buku Teks
Sinnott-Armstrong, Walter, author
Oxford University Press, 2016
eBooks
Taylor, John E.
MIT Press, 1999
Buku Teks
Holt, Edwin B. (Edwin Bissell), 1873-1946
Macmillan, 1974
Buku Teks
Sturgeon, Scott, 1961-, author
Routledge, 2000
Buku Teks