For more than six decades, and for thousands of students, Introduction to Logic has been the gold standard in introductory logic texts. In this fifteenth edition, Carl Cohen and Victor Rodych update Irving M. Copi's classic text, improving on its many strengths and introducing new and helpful material that will greatly assist both students and instructors. In particular, chapters 1, 8, and 9 have been greatly enhanced without disturbing the book's clear and gradual pedagogical approach. Specifically: Chapter 1 now uses a simpler and better definition of "deductive validity," which enhances the rest of the book (especially chapters 1 and 8-10, and their new components). Chapter 8 now has: Simpler definitions of "simple statement" and "compound statement" More and more detailed examples of the Complete Truth-Table Method. Chapter 9 now has: A detailed, step-by-step account of the Shorter Truth-Table Method (with detailed step-by-step examples for conclusions of different types) A more complete and detailed account of Indirect Proof A detailed justification for Indirect Proof treating each of the three distinct ways in which an argument can be valid A new section on Conditional Proof, which complements the 19 Rules of Inference and Indirect Proof Explications of proofs of tautologies using both Indirect Proof and Conditional Proof A new section at the end of the chapter explaining the important difference between sound and demonstrative arguments. The Appendices now include: A new appendix on making the Shorter Truth-Table Technique (STTT) more efficient by selecting the most efficient sequence of STTT steps A new appendix on Step 1 calculations for multiple-line shorter truth tables A new appendix on unforced truth-value assignments, invalid arguments, and Maxims III-V. In addition, a Companion Website will offer: for Students: A Proof Checker Complete Truth Table Exercises Shorter Truth-Table Exercises A Truth-Table Video Venn Diagram Testing of Syllogisms Hundreds of True/False and Multiple Choice Questions for Instructors: An Instructor's Manual A Solutions Manual www.routledge.com/cw/9781138500860