 On the other hand, intentional states such as beliefs, thoughts, and desires (sometimes called “propositional attitudes”) have often been thought to be easier to characterize functionally than experiential states such as pains and color experiences (but not always: see Searle 1992, G. Strawson 1994, Horgan and Tienson 2002, Kriegel 2003, and Pitt 2008, who suggest that intentional states have qualitative character as well). We can begin by characterizing beliefs as (among other things) states produced in certain ways by sense-perception or inference from other beliefs, and desires as states with certain causal or counterfactual relations to the system's goals and needs, and specify further how (according to the relevant common sense or empirical theory) beliefs and desires tend to interact with one another, and other mental states, to produce behavior. 