THE PURPOSE OF FACTOR ANALYSISA factor problem starts with the hope or conviction that a certain domain is not so chaotic as it looks. The object of factor analysis is to discover the principal dimensions or categories of mentality and to indicate the directions along which they may be studied by experimental laboratory methods. Factor analysis is not restricted by assumptions regarding the nature of the factors, whether they be physiological or social, elemental or complex, correlated or uncorrelated. It assumes that a variety of phenomena within the domain are related and that they are determined, at least in part, by a relatively small number of functional unities, or factors. The factors may be called by different names, such as causes, faculties, parameters, functional unities, abilities, independent measurements, experimentally independent effects. The name for a factor depends on the context, on one's philosophical preferences and manner of speech, and on how much one already knows about the domain to be investigated. The factors in psychological investigations are not ordinarily to be thought of as elemental things which are present or absent, like heads or tails in the tossing of coins.On previous occasions I have stated that factor analysis has its principal usefulness at the borderline of science and that it is naturally superseded as quickly as possible by rational formulations in terms of the science involved. Factor analysis is useful especially in