ABSTRACT
The thesis that some central thought processes might be modular gets support from a wealth of recent work tending to show that many basic conceptual thought processes, found in every culture and in every fully developed human, are governed by domain-specific competences. An evolutionary account of the emergence of a conceptual module in a mind that had known only perceptual processes is simple enough to imagine. Its demodularization would be much harder to explain. The 'domains' of modules may vary in character and in size: there is no reason to expect each domain-specific module to handle a domain of comparable size. The input to the first conceptual modules to have appeared in cognitive evolution must have come from the perceptual modules. The output of perceptual and conceptual modules is in the form of conceptual representations. Perceptual modules categorize distal stimuli and must each have therefore the conceptual repertoire needed for the output categorizations of which they are capable.
