Logic is essential to correct reasoning and also has important theoretical applications in philosophy, computer science, linguistics, and mathematics. This book provides an exceptionally clear introduction to classical logic, with a unique approach that emphasizes both the hows and whys of logic. Here Nicholas Smith thoroughly covers the formal tools and techniques of logic while also imparting a deeper understanding of their underlying rationales and broader philosophical significance. In addition, this is the only introduction to logic available today that presents all the major forms of proof--trees, natural deduction in all its major variants, axiomatic proofs, and sequent calculus. The book also features numerous exercises, with solutions available on an accompanying website. Logic is the ideal textbook for undergraduates and graduate students seeking a comprehensive and accessible introduction to the subject. * Provides an essential introduction to classical logic * Emphasizes the how and why of logic * Covers both formal and philosophical issues * Presents all the major forms of proof--from trees to sequent calculus * Features numerous exercises, with solutions available at http://www-personal.usyd.edu.au/~njjsmith/lawsoftruth * The ideal textbook for undergraduates and graduate students