The Language of First-order Logic is a complete introduction to first-order symbolic logic, consisting of a computer program and a text. The program, an aid to learning and using symbolic notation, allows one to construct symbolic sentences and possible worlds, and verify that a sentence is well-formed. The truth or falsity of a sentence can be determined by playing a deductive game with the computer. The text covers four areas: propositional logic, quantifier logic, the application of first-order logic to set theory and induction, and advanced topics. Hundreds of exercises and problems are included. This revised and expanded edition includes an extensive series of translation exercises to and from ordinary language, and proof exercises using ordinary language. The new release of the Macintosh software, Tarski's World 4.O, has a new sentence window and includes a "verify all" command for quickly checking a set of sentences in a world.John Etchemendy is the author of 'The Language of First-Order Logic : Including the Macintosh Program Tarski's World 4.0/Book and Disk (Csli Lecture Notes, No 23)', published 1993 under ISBN 9780937073995 and ISBN 0937073997.