Now in it's fourth edition, this classic work on logic presents the student with a clear, concise introduction to the subject of logic and its apllications. The first part of the book introduces the concepts and principles which make up the elements of logic, demonstrating that the concepts of logic are found in all branches of mathematics, and that logical laws are constantly applied in mathematical reasoning. The book goes on to show the applications of logic in mathematical theory building using concrete examples, drawing upon the concepts and principles presented in the first section. An introduction to the theory of real numbers is also presented. Exercises are included, designed to assist in the assimilation of the concepts and principles. Throughout the conceptual side or logic is stressed. Thoroughly revised by the author's son, the book remains a fundametal guide to modern mathematica logic and is a very important addition to this highly successful series.