Review of Newell, Unified Theories of Cognition

For Artificial Intelligence, 59, (1-2), 285-294, Feb. 1993. Reprinted in Clancey, Smoliar and Stefik, eds., Contemplating Minds: A Forum for Artificial Intelligence, MIT Press.

Daniel C. Dennett
Center for Cognitive Studies
Tufts University

Review of Allen Newell, Unified Theories of Cognition

The time for unification in cognitive science has arrived, but who should lead the charge? The immunologist-turned-neuroscientist Gerald Edelman (1989, 1992) thinks that neuroscientists should lead--or more precisely that he should (he seems to have a low opinion of everyone else in cognitive science). Someone might think that I had made a symmetrically opposite claim in Consciousness Explained (Dennett, 1991): philosophers (or more precisely, those that agree with me!) are in the best position to see how to tie all the loose ends together. But in fact I acknowledged that unifying efforts such as mine are proto-theories, explorations that are too metaphorical and impressionistic to serve as the model for a unified theory. Perhaps Newell had me in mind when he wrote in his introduction (p.16) that a unified theory "can't be just a pastiche, in which disparate formulations are strung together with some sort of conceptual bailing wire," but in any case the shoe more or less fits, with some pinching. Such a "pastiche" theory can be a good staging ground, however, and a place to stand while considering the strengths and weaknesses of better built theories. So I agree with him.

It is not just philosophers' theories that need to be made honest by modeling at this level; neuroscientists' theories are in the same boat. For instance, Gerald Edelman's (1989) elaborate theory of "re-entrant" circuits in the brain makes many claims about how such re-entrants can accomplish the discriminations, build the memory structures, coordinate the sequential steps of problem solving, and in general execute the activities of a human mind, but in spite of a wealth of neuroanatomical detail, and enthusiastic and often plausible assertions from Edelman, we won't know what his re-entrants can do--we won't know that re-entrants are the right way to conceive of the functional neuroanatomy--until they are fashioned into a whole cognitive architecture at the grain-level of Act* or Soar and put through their paces. (Dennett, 1991, p.268)

So I begin with a ringing affirmation of the central claim of Newell's book. Let's hear it for models like Soar. Exploring whole cognitive systems at roughly that grain-level is the main highway to unification. I agree, moreover, with the reasons he offers for his proposal (see especially pages 17-36). But in my book I also alluded to two reservations I have with Newell's program without spelling out or defending either of them. This is obviously the time to make good on those promissory notes or recant them.

(The whole paper is now available in Daniel Dennett, Brainchildren, Essays on Designing Minds, MIT Press and Penguin, 1998.)