rational psychology the a priori study of the mind. This was a large component of eighteenthand nineteenth-century psychology, and was contrasted by its exponents with empirical psychology, which is rooted in contingent experience. The term ‘rational psychology’ may also designate a mind, or form of mind, having the property of rationality. Current philosophy of mind includes much discussion of rational psychologies, but the notion is apparently ambiguous. On one hand, there is rationality as intelligibility. This is a minimal coherence, say of desires or inferences, that a mind must possess to be a mind. For instance, Donald Davidson, many functionalists, and some decision theorists believe there are principles of rationality of this sort that constrain the appropriate attribution of beliefs and desires to a person, so that a mind must meet such constraints if it is to have beliefs and desires. On another pole, there is rationality as justification. For someone’s psychology to have this property is for that psychology to be as reason requires it to be, say for that person’s inferences and desires to be supported by proper reasons given their proper weight, and hence to be justified. Rationality as justification is a normative property, which it would seem some minds lack. But despite the apparent differences between these two sorts of rationality, some important work in philosophy of mind implies either that these two senses in fact collapse, or at least that there are intervening and significant senses, so that things at least a lot like normative principles constrain what our psychologies are. See also PHILOSOPHY OF MIND. J.R.M.