Mediaeval Logic and Philosophy  
   Resource maintained by Paul Vincent Spade at Indiana University.
   http://pvspade.com/Logic/

The Summulae of John Buridan  
   A critical introduction by Gyula Klima.
   http://www.fordham.edu/gsas/phil/klima/Intro.htm

Medieval Theories of Analogy  
   Entry in the Stanford Encyclopaedia of Philosophy, by E. Jennifer Ashworth.
   http://plato.stanford.edu/entries/analogy-medieval/

Medieval Theories of Modality  
   Article at the Stanford Encyclopaedia of Philosophy.
   http://plato.stanford.edu/entries/modality-medieval/

Scholastic Logic  
   Chapter Two of Joseph Perrier's "The Revival of Scholastic Philosophy in the Nineteenth Century" (1909).
   http://www.nd.edu/Departments/Maritain/etext/perrier2.html

Scholasticism  
   Online text by Joseph Rickaby (1908).
   http://www.nd.edu/Departments/Maritain/etext/scholas1.htm

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

Square of Opposition  
   Article in the Stanford Encyclopaedia of Philosophy, by Terence Parsons.
   http://plato.stanford.edu/entries/square/

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

Aristotle's Logic  
   Introductory article by Garth Kemerling.
   http://www.philosophypages.com/hy/2n.htm

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/

On Dialectic  
   By St. Augustine. Latin original together with translation by J. Marchand.
   http://www.georgetown.edu/faculty/jod/texts/dialecticatrans.html

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