A family of related objections to associationism can be interpreted as variations on this theme. For example, problems of productivity, compositionality, and systematicity for associationist theorizing appear to be variants of the problem of predication (for more on these  specific issues see the entries on the  Language of Thought Hypothesis and   on compositionality). If association doesn’t add any additional structure to the mental representations that get associated, then it is hard to see how it can explain the compositionality of thought, which relies on structures that specify relations among intentional contents. Compositionality requires that the meaning of a complex thought is determined by the meanings of its simple constituents along with their syntactic arrangements. The challenge to associationism is to explain how an associative mechanism can give rise to the syntactic structures necessary to distinguish a complex thought like   birds fly from the temporal succession of two simple thoughts   birds and  fly. Since the compositionality of thought is posited to undergird the productivity of thought (thinkers’ abilities to think novel sentences of arbitrary lengths, e.g.,  green birds fly,  giant green birds fly, cuddly giant green birds fly, etc.), associationism has problems explaining productivity.