This book is an introduction to reasoning in psychology, including a brief treatment of deductive reasoning and an extensive treatment of inductive reasoning. It also covers basic issues in the philosophy of science as they relate to psychology. Topics include deductive and inductive argumentation, Mill's Methods of Induction, falsificationism (Popperian and Lakatos' research programmes), basic philosophy of induction (Hume's problem and attempted solutions), Bayes's Theorem, basic probability theory, and reading basic graphs (histograms) in probability. The book can be read as a guide on its own or it could function as a textbook in an introductory course on induction and the philosophy of science for psychology majors. The professor should be able to make it apply to any other science.