For a pure associationist, association is “semantically transparent” (see Fodor 2003), in that it purports to add no additional structure to thoughts. When a simple concept, X and a simple concept Y, become associated one acquires the associative structure X/Y. But X/Y has no additional structure on top of their contents. Knowing that X and Y are associated amounts to knowing a causal fact: that activating Xs will bring about the activation of Ys and vice versa. However, so the argument goes, some of our thoughts appear to have more structure than this: the thought  birds fly predicates the property of flying onto birds. The task for the associationist is to explain how associative structures can distinguish a thinker who has a single (complex) thought  birds fly from a thinker who conjoins two simple thoughts in an associative structure where one thought,  birds, is immediately followed by another,  fly. As long as the two simple thoughts are reliably causally correlated so that, for a thinker, activations of birds regularly brings about  fly, then that thinker has the associative structure  birds/fly. Yet it appears that thinker hasn’t yet had the thought  birds fly. The problem of predication is explaining how a purely associative mechanism could eventuate in complex thoughts. In Fodor’s terms the problem boils down to how association, a causal relation among mental representations, can affect predication, a relation among intentional contents (Fodor 2003).