AbstractThis article begins with an account of logic, and of how logicians formulate formal rules of inference for the sentential calculus, which hinges on analogs of negation and the connectivesif, or, andand. It considers the various ways in which computer scientists have written programs to prove the validity of inferences in this and other domains. Finally, it outlines the principal psychological theories of how human reasoners carry out deductions. Copyright © 2009 John Wiley & Sons, Ltd.This article is categorized under:Psychology > Reasoning and Decision Making