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

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

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.

12th Century Logic - A medieval logic resource, maintained by Iwakuma Yukio. Includes many online texts and resources, as well as exhaustive census of medieval logic manuscripts.

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.

The Organon - Set of the texts of Aristotle's logic, organised by Roger Bishop Jones.

Aristotle's Logic - Introductory article by Garth Kemerling.

19th Century Logic between Philosophy and Mathematics - Article by Volker Peckhaus.