Compositionality: A Connectionist Variation on a Classical Theme

Connectionism has been attacked on the grounds that it does not employ compo-sitionally structured representations (e.g., Fodor 8 Pylyshyn, 1988). This article develops the response that Connectionist models can, and in fact sometimes do, employ compositionally structured representations without, thereby. simply implementing a Classical " Language of Thought. " Focusing on the mode of combination employed in constructing representations, it distinguishes concotenative compositionality, essential to the Classical approach. from a merely functional counterpart increasingly common in Connectionist research. On the basis of this distinction it is possible to demonstrate that Connectionist representations can be compositional without being Classical. and further, that Fodor and Pylyshyn's supposedly conclusive arguments in fovor of the Classical approach do not in fact support that approach over the Connectionist alternative (as opposed lo an " osso-ciotionist " straw man). Must mental representations be structured objects? If so, in what sense? These very general questions, never far below the surface in both the theory and practice of cognitive science, have arisen once again in the guise of a clash between defenders of mainstream symbolic or " Classical " orthodoxy, and advocates of the rival Connectionist approach to the modeling of cogni-tion. Classicalists, such as Fodor and Pylyshyn (1988), have argued that the explanation of cognition requires representations iith a combinatorial syntax and semantics; Connectionism is doomed, it is claimed, unless it finds a way to implement such representations. Smolensky, meanwhile, has proposed a formidable defense: Connectionist representations can be composi-tional without being strictly combinatorial in the Classical sense, and on this basis Connectionism can account for cognition without needing to implement a " Language of Thought " (Smolensky, 1987b, 1988). There is at least one basic point of agreement among the various parties: In order to exhibit any reasonably sophisticated cognitive functions, a system This article was much improved in light of the numerous thoughtful comments from the reviewers for Cognitive Science.