Reductio Ad Absurdum

Reductio Ad Absurdum

The crowbar of rational inquiry, the great lever that enforces consistency, is reductio ad absurdum—literally, reduction (of the argument) to absurdity. You take the assertion or conjecture at issue and see if you can pry any contradictions (or just preposterous implications) out of it. If you can, that proposition has to be discarded or sent back to the shop for retooling. We do this all the time without bothering to display the underlying logic: “If that’s a bear, then bears have antlers!” or “He won’t get here in time for supper unless he can fly like Superman.” When the issue is a tricky theoretical controversy, the crowbar gets energetically wielded, but here the distinction between fair criticism and refutation by caricature is hard to draw. Can your opponent really be so stupid as to believe the proposition you have just reduced to absurdity with a few deft moves? I once graded a student paper that had a serendipitous misspelling, replacing “parity” with “parody,” creating the delicious phrase “by parody of reasoning,” a handy name, I think, for misbegotten reductio ad absurdum arguments, which are all too common in the rough-and-tumble of scientific and philosophical controversy.

I recall attending a seminar on cognitive science at MIT some years ago, conducted by the linguist Noam Chomsky and the philosopher Jerry Fodor, in which the audience was regularly regaled with hilarious refutations of cognitive scientists from elsewhere who did not meet with their approval. On this day, Roger Schank, the director of Yale University’s artificial intelligence laboratory, was the bête noir, and if you went by Chomsky’s version, Schank had to be some kind of flaming idiot. I knew Roger and his work pretty well, and though I had disagreements of my own with it, I thought that Noam’s version was hardly recognizable, so I raised my hand and suggested that perhaps he didn’t appreciate some of the subtleties of Roger’s position. “Oh no,” Noam insisted, chuckling. “This is what he holds!” And he went back to his demolition job, to the great amusement of those in the room. After a few more minutes of this I intervened again. “I have to admit,” I said, “that the views you are criticizing are simply preposterous,” and Noam grinned affirmatively, “but then what I want to know is why you’re wasting your time and ours criticizing such junk.” It was a pretty effective pail of cold water.

What about my own reductios of the views of others? Have they been any fairer? Here are a few to consider. You decide. The French neuroscientist Jean-Pierre Changeux and I once debated neuroscientist Sir John Eccles and philosopher Sir Karl Popper about consciousness and the brain at a conference in Venice. Changeux and I were the materialists (who maintain that the mind is the brain), and Popper and Eccles the dualists (who claim that a mind is not a material thing like a brain, but some other, second kind of entity that interacts with the brain). Eccles had won the Nobel Prize many years earlier for the discovery of the synapse, the microscopic gap between neurons that glutamate molecules and other neurotransmitters and neuromodulators cross trillions of times a day. According to Eccles, the brain was like a mighty pipe organ and the trillions of synapses composed the keyboards. The immaterial mind—the immortal soul, according to Eccles, a devout Catholic—played the synapses by somehow encouraging quantum-level nudges of the glutamate molecules. “Forget all that theoretical discussion of neural networks and the like; it’s irrelevant rubbish,” he said. “The mind is in the glutamate!” When it was my turn to speak, I said I wanted to be sure I had understood his position. If the mind was in the glutamate and I poured a bowl of glutamate down the drain, would that not be murder? “Well,” he replied, somewhat taken aback, “it would be very hard to tell, wouldn’t it?”[1]

You would think that Sir John Eccles, the Catholic dualist, and Francis Crick, the atheist materialist, would have very little in common, aside from their Nobel Prizes. But at least for a while their respective views of consciousness shared a dubious oversimplification. Many nonscientists don’t appreciate how wonderful oversimplifications can be in science; they can cut through the hideous complexity with a working model that is almost right, postponing the messy details until later. Arguably the best use of “over”-simplification in the history of science was the end run by Crick and James Watson to find the structure of DNA while Linus Pauling and others were trudging along trying to make sense of all the details. Crick was all for trying the bold stroke just in case it solved the problem in one fell swoop, but of course that doesn’t always work. I was once given the opportunity to demonstrate this at one of Crick’s famous teas at La Jolla. These afternoon sessions were informal lab meetings where visitors could raise issues and participate in the general discussion. On this particular occasion Crick made a bold pronouncement: it had recently been shown that neurons in cortical area V4 “cared about” (responded differentially to) color. And then he proposed a strikingly simple hypothesis: the conscious experience of red, for instance, was activity in the relevant red-sensitive neurons of that retinal area. Hmm, I wondered. “Are you saying, then, that if we were to remove some of those red-sensitive neurons and keep them alive in a petri dish, and stimulate them with a microelectrode, there would be consciousness of red in the petri dish?” One way of responding to a proffered reductio is to grasp the nettle and endorse the conclusion, a move I once dubbed outsmarting, since the Australian philosopher J. J. C. Smart was famous for saying that yes, according to his theory of ethics, it was sometimes right to frame and hang an innocent man! Crick decided to outsmart me. “Yes! It would be an isolated instance of consciousness of red!” Whose consciousness of red? He didn’t say. He later refined his thinking on this score, but still, he and neuroscientist Christof Koch, in their quest for what they called the NCC (the neural correlates of consciousness), never quite abandoned their allegiance to this idea.

Perhaps yet another encounter will bring out better what is problematic about the idea of a smidgen of consciousness in a dish. The physicist and mathematician Roger Penrose and the anesthesiologist Stuart Hameroff teamed up to produce a theory of consciousness that depended, not on glutamate, but on quantum effects in the microtubules of neurons. (Microtubules are tubular protein chains that serve as girders and highways inside the cytoplasm of all cells, not just neurons.) At Tucson II, the second international conference on the science of consciousness, after Hameroff’s exposition of this view, I asked from the audience, “Stuart, you’re an anesthesiologist; have you ever assisted in one of those dramatic surgeries that replaces a severed hand or arm?” No, he had not, but he knew about them. “Tell me if I’m missing something, Stuart, but given your theory, if you were the anesthesiologist in such an operation you would feel morally obliged to anesthetize the severed hand as it lay on its bed of ice, right? After all, the microtubules in the nerves of the hand would be doing their thing, just like the microtubules in the rest of the nervous system, and that hand would be in great pain, would it not?” The look on Stuart’s face suggested that this had never occurred to him. The idea that consciousness (of red, of pain, of anything) is some sort of network property, something that involves coordinated activities in myriads of neurons, initially may not be very attractive, but these attempts at reductios may help people see why it should be taken seriously.

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[1] My other indelible memory of that conference was of Popper’s dip in the Grand Canal. He slipped getting out of the motorboat at the boathouse of the Isola di San Giorgio and fell feet first into the canal, submerged up to his knees before being plucked out and set on the pier by two nimble boatmen. The hosts were mortified and ready to rush back to the hotel to get nonagenarian Sir Karl a dry pair of trousers, but the pants he was wearing was the only pair he’d brought—and he was scheduled to lead off the conference in less than half an hour! Italian ingenuity took over, and within about five minutes I enjoyed an unforgettable sight: Sir Karl, sitting regally on a small chair in the exact middle of a marble-floored, domed room (Palladio designed it) surrounded by at least half a dozen young women in miniskirts, on their knees, plying his trouser legs with their hairdryers. The extension cords stretched radially to the walls, making of the tableau a sort of multicolored human daisy, with Sir Karl, unperturbed but unsmiling, in the center. Fifteen minutes later he was dry and pounding his fist on the podium to add emphasis to his dualistic vision.