Intelligence has three facets. There are numerous intellectual abilities, but they fall neatly into a rational system.

In this limited space I have attempted to convey information regarding progress in discovering the nature of human intelligence. By intensive factor-analytic investigation, mostly within the past 20 years, the multifactor picture of intelligence has grown far beyond the expectations of those who have been most concerned. A comprehensive, systematic theoretical model known as the "structure of intellect" has been developed to put rationality into the picture. The model is a cubical affair, its three dimensions representing ways in which the abilities differ from one another. Represented are: five basic kinds of operation, four substantive kinds of information or "contents," and six formal kinds of information or "products," respectively. Each intellectual ability involves a unique conjunction of one kind of operation, one kind of content, and one kind of product, all abilities being relatively independent in a population, but with common joint involvement in intellectual activity. This taxonomic model has led to the discovery of many abilities not suspected before. Although the number of abilities is large, the 15 category constructs provide much parsimony. They also provide a systematic basis for viewing mental operations in general, thus suggesting new general psychological theory. The implications for future intelligence testing and for education are numerous. Assessment of intellectual qualities should go much beyond present standard intelligence tests, which seriously neglect important abilities that contribute to problem-solving and creative performance in general. Educational philosophy, curriculum-building, teaching procedures, and examination methods should all be improved by giving attention to the structure of intellect as the basic frame of reference. There is much basis for expecting that various intellectual abilities can be improved in individuals, and the procedures needed for doing this should be clear.