Mediaeval Logic and Philosophy
Resource maintained by Paul Vincent Spade at Indiana University.

The Summulae of John Buridan
A critical introduction by Gyula Klima.

Medieval Theories of Analogy
Entry in the Stanford Encyclopaedia of Philosophy, by E. Jennifer Ashworth.

Medieval Theories of Modality
Article at the Stanford Encyclopaedia of Philosophy.

Scholastic Logic
Chapter Two of Joseph Perrier's "The Revival of Scholastic Philosophy in the Nineteenth Century" (1909).

Scholasticism
Online text by Joseph Rickaby (1908).

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.

Square of Opposition
Article in the Stanford Encyclopaedia of Philosophy, by Terence Parsons.

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.

Aristotle's Logic
Introductory article by Garth Kemerling.

Peter of Spain (Petrus Hispanus)
Life and work of 13th century logician and author of the Tractatus; from the Stanford Encyclopedia by Joke Spruyt.

On Dialectic
By St. Augustine. Latin original together with translation by J. Marchand.

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.