The explosive progress of logic, since Frege, has produced applications in linguistics, mathematics and computer science. Students and practitioners of any of these fields, and of philosophy, will find this book an excellent reference or introduction. Now expanded to include non-classical logic, logic for the computer, and more. The central concepts are explained as they come into play in informal writing and conversation --argument, validity, relevance, and so on. This study guide progresses to concepts such as probability calculus.