This glossary is confined, with few exceptions, to terms used in formal logic, set theory, and related areas. No attempt has been made to cover what is often called "inductive logic," although several terms in this field have been included for the convenience of the reader.

It should be noted that many topics dealt with very briefly here are treated in full in various other entries in this encyclopedia. Cross references to these will be enclosed in quotation marks; cross references to other glossary entries will be indicated by boldface italics (e.g., "see relation").

Abduction

(1) A syllogism whose major premise is known to be true but whose minor premise is merely probable. (2) C. S. Peirce's name for the type of reasoning that yields from a given set of facts an explanatory hypothesis for them.

Abstraction

(1) In traditional logic, the process of...