A Model Science

George Miller

  • Mental Models: Towards a Cognitive Science of Language, Inference and Consciousness by P.N. Johnson-Laird
    Cambridge, 513 pp, £27.50, August 1983, ISBN 0 521 24123 5

Cognition has become fashionable. Half a dozen academic disciplines are currently scrambling to establish ownership. The philosophers, who got there first, are being jostled by empiricists, but are relaxing none of their traditional claims. To psychologists, cognition is a ‘problem’ that only they can analyse experimentally. Social anthropologists feel that their concern for culture gives them some special claim to cognition. Computer scientists who create artificially intelligent systems now freely define cognition in their own likeness. Special cognitive intuitions about language provide basic data for linguists. Even neuroscientists now speak of cognitive brain processes. All put forward their favourite entitlements.

Until very recently each discipline proceeded as though its enterprise were the only one of consequence. Each knows that the others exist, but has little appreciation of potential conflicts or redundancies. The subject has become a village where every door bears a sign reading ‘COGNITION: Main Entrance’. Innocents wandering into town are inevitably confused by the different messages echoing from every side.

A new idea has lately invaded this community, an idea of federation and co-operation. It is called Cognitive Science, in the singular, and it embraces all those parts of the contending disciplines that have serious claims on the subject. So far, computer scientists have taken the lead, but cognitive psychologists and theoretical linguists are not far behind. Evidence that this federation might succeed has now taken shape in P.N. Johnson-Laird’s new book, Mental Models, which is surely the most authoritative guide to this intellectual territory now available. Its origin was a series of seven talks given at Stanford University early in 1980, but in the present version many explanations of the technical notions it draws upon have been added. Nowhere else have so many of the seminal ideas of this new field been pulled together and their relations explored. Not that there have not been excellent treatments of the individual fields – books on artificial intelligence, on cognitive psychology, on theoretical linguistics, on the philosophy of mind – at all levels of sophistication. What has been lacking, and what Johnson-Laird has come surprisingly close to providing, is a book that moves freely across territorial boundaries, a book addressed to everyone who has a sincere interest in how the mind works.

Taken for granted in most of the recent fuss over cognition is a questionable analytic assumption that those aspects of mental life concerned with knowing can be painlessly detached from those concerned with feeling or willing. This assumption seems to have originated in the 18th century’s tripartite division of the mind into cognitive, emotive and conative faculties, but in the 19th century it became little more than a manner of speaking as theories of the association of ideas replaced theories of mental faculties. At first glance, the reappearance of cognition on the scientific landscape of the 20th century might seem to be a regressive step. But not so. Today the separation of cognition from other mental phenomena is seen as a necessary idealisation, similar to ignoring wind resistance while working out the laws of gravitation. Only time will tell whether the idealisation is a good one, but meanwhile many cognitive scientists take comfort from the existence of that most purely cognitive of all systems – the modern, high-speed, stored-program, digital computer.

The paradox implicit in this situation – in mentalism revitalised by advances in mechanism – has been noted more than once. But it is a new brand of mentalism. What the computer provides that has completely redefined the study of cognition is, first, a language (or family of languages) in which very detailed theories of cognitive functioning can be stated, and, second, a general type of mechanism whereby the implications of those theories can be demonstrated. Working out the consequences of this redefinition is a critical assignment for the new science of cognition.

The most immediate consequence is that henceforth it must be possible to formulate cognitive theories as computer programs. More precisely, they must be formulable as ‘effective procedures’ for performing mental computations, theoretical descriptions from which programs for particular computers might be constructed. ‘If the long promised Newtonian revolution in the study of cognition is to occur,’ Johnson-Laird remarks, ‘then qualitative explanations will have to be abandoned in place of effective procedures.’

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