Peirce argues that each genus of inference - deduction, induction, and abduction - has a different truth-producing virtue. An inference is valid just in case the procedure used in fact has the truth-producing virtue claimed for it and the person making the inference adheres to the procedure. In successive chapters, this book shows how Peirce supports the thesis that these genera of inference have the truth-producing virtues claimed for them and how Peirce responds to objections. Among the objections given consideration are the liar paradox, Hume's problem of induction, Goodman's new riddle of induction, that this may be a chance world, and that we are incapable of conceiving the true hypothesis. The book defends several controversial theses, including that Peirce does not so strongly object to Bayesianism as is sometimes claimed and that prior to 1900 Peirce had no explicit theory of abduction. It also proposes a novel account of abduction.