Fallacies, by William of Ockham (AD 1287-1347), is the last book (Part 3, Book 4) of the Summa Logicae (Summary of Logic), a medieval textbook on syllogistic logic which is divided into three parts: terms, propositions and syllogisms, broadly speaking.

Fallacies is the medieval nominalist¿s response to Aristotle¿s Sophistical Refutations (De Sophisticis Elenchis). It treats of the fallacies of equivocation, amphibology, composition and division, accent, figure of speech, secundum quid et simpliciter, among others.

A Franciscan monk, philosopher and logician, William of Ockham is widely considered the father of nominalism. The Summa Logicae is his principal treatise on the subject. From a nominalistic point of view, it takes a fresh look at Aristotle¿s Categories, Interpretation and Topics as contained in the Organon; and it rejects the idea of universals as things having an independent existence outside the mind (as originally advanced by Plato).