Artikel Jurnal
Ayer, A. J. (Alfred Jules), 1910-1989, author
Penguin Books, 1956
Buku Teks
Wojciechowski, Jerzy A., author
Council for research in values and philosophy, [Date of publication not identified]
Buku Teks
O`Brien, Dan, author
Polity Press, 2006
Buku Teks
Morton, Adam, author
Blackwell, 1997
Buku Teks