 The first of these views maintains that concepts are psychological entities, taking as its starting point the representational theory of the mind (RTM). According to RTM, thinking occurs in an internal system of representation. Beliefs and desires and other propositional attitudes enter into mental processes as internal symbols. For example, Sue might believe that Dave is taller than Cathy, and also believe that Cathy is taller than Ben, and together these may cause Sue to believe that Dave is taller than Ben. Her beliefs would be constituted by mental representations that are about Dave, Cathy and Ben and their relative heights. What makes these beliefs, as opposed to desires or other psychological states, is that the symbols have the characteristic causal-functional role of beliefs. (RTM is usually presented as taking beliefs and other propositional attitudes to be relations between an agent and a mental representation (e.g., Fodor 1987). But given that the relation in question is a matter of having a representation with a particular type of functional role, it is simpler to say that occurrent beliefs just are mental representations with this functional role.)