How the Physical Symbols Systems Hypothesis and the Modularity Hypothesis are Reformulations of each Other

Abstract

This paper examines the relationship between two influential theories in cognitive science and philosophy of mind: Fodor’s modularity of mind hypothesis and the Physical Symbol System Hypothesis (PSSH) proposed by Newell and Simon. Although modularity is traditionally framed as a theory of cognitive architecture and the PSSH as a computational account of intelligence, this paper argues that the distinction between them is largely conceptual rather than substantive. The central claim is that modularity and the PSSH are, in effect, reformulations of the same un-derlying theoretical commitment. The analysis begins with a critical review of Fodor’s defining criteria for modules, such as domain specificity, mandatory operation, informational encapsula-tion, and shallow outputs. While these conditions were intended to provide an empirically gro-unded account of mental organization, many of them remain vague or metaphorical. Neverthe-less, taken together, they imply that cognitive processes must be decomposable into functionally distinct components with standardized input–output relations. Such decomposability presupposes the manipulation of structured representations. From this, the paper derives its first key claim: any modular cognitive process necessarily involves symbolic processing. Modules can only func-tion if their outputs are formatted in a way that allows systematic recombination and communica-tion with other components. This requirement aligns directly with the notion of a physical symbol system. Modularity, therefore, implicitly assumes the symbolic ontology articulated explicitly by the PSSH. The argument then proceeds in the opposite direction. If the PSSH is correct in clai-ming that a physical symbol system is sufficient for general intelligent action, then general intelli-gence must be implementable via organized subsystems that operate on specific classes of sym-bols. At the functional level, these subsystems correspond to modules. This establishes a bidirec-tional equivalence: modularity entails symbolic processing, and symbolic processing entails mo-dular realizability. The paper concludes that long-standing debates opposing modularity to sym-bolic approaches rest on a false dichotomy, and that recognizing their equivalence offers a clearer framework for understanding both human and artificial intelligence.