The mathematical and philosophical origins of "analogy" are described and their influence on the thinking of intelligence theorists is traced. Theories of intelligence and cognition bearing on analogical reasoning are examined, specifically those of Spearman, Thorndike, Guilford and Piaget. The analogy test item is shown to be a paradigm for Spearman's theory. The relevance of Piaget's theory of formal reasoning to an analysis of analogical reasoning is detailed. Data and findings about analogy tests are summarized. Support is adduced for Guilford's factorial interpretation of analogy test scores within the Structure of Intellect. (Author)