Aristotle's Reform of Paideia Article by Evelyn Barker, arguing that the principal aim of Aristotle's Organon was to reform the contemporary paedagogical role of dialectic. http://www.bu.edu/wcp/Papers/Anci/AnciBark.htm
Logic Entry in the Catholic Encyclopaedia (1917), dominated by a historical survey from Indian and Pre-Aristotelian philosophy to the Logic of John Stuart Mill. http://www.newadvent.org/cathen/09324a.htm
Mediaeval Logic and Philosophy Resource maintained by Paul Vincent Spade at Indiana University. http://pvspade.com/Logic/
Peter of Spain (Petrus Hispanus) Life and work of 13th century logician and author of the Tractatus; from the Stanford Encyclopedia by Joke Spruyt. http://plato.stanford.edu/entries/peter-spain/
Syllogistic logic online This site contains an online program for studying Aristotle's syllogistic logic. The theory of Aristotle's ancient logic is also presented. http://aristotelianlogic.glashoff.net