Abstract: To be an intentional system, to be a system which has beliefs and desires and the like, is to be exposed perceptually to a certain sort of environment and to interact with that environment in a way that makes sense, and makes sense nonaccidentally, in belief–desire terms. There are regularities characteristic of beliefs and desires, regularities that dictate both the effect of certain sort of evidence on what beliefs and desires are maintained, and the effect of certain sorts of belief–desire profiles on what responses are evinced. Those regularities will typically identify what it is to be evidentially rational in the attitudes one holds and responsively rational in the responses one makes, though they may also point us toward obstacles that get in the way of rational performance. A system will count as an intentional agent to the extent that its interactions with its environment, or at least some of its interactions, are governed by such regularities.

Keywords: belief, desire, intentional agency, intentionality, rationality,