1. Hilary Putnam, “The Meaning of Meaning,” in The Twin Earth Chronicles, ed. Andrew Pessin and Sanford Goldberg (M. E. Sharpe, Inc., 1996), 3–52.
217
Brain Breakthrough! It’s Made of Neurons!
In an amazing breakthrough, a multinational team of scientists led by Nobel laureate Santiago Ramón y Cajal announced that the brain is composed of a ridiculously complicated network of tiny cells connected to each other by infinitesimal threads and branches.
The multinational team—which also includes the famous technician Antonie van Leeuwenhoek, and possibly Imhotep, promoted to the Egyptian god of medicine—issued this statement:
“The present discovery culminates years of research indicating that the convoluted squishy thing inside our skulls is even more complicated than it looks. Thanks to Cajal’s application of a new staining technique invented by Camillo Golgi, we have learned that this structure is not a continuous network like the blood vessels of the body, but is actually composed of many tiny cells, or ‘neurons,’ connected to one another by even more tiny filaments.
“Other extensive evidence, beginning from Greek medical researcher Alcmaeon and continuing through Paul Broca’s research on speech deficits, indicates that the brain is the seat of reason.
“Nemesius, the Bishop of Emesia, has previously argued that brain tissue is too earthy to act as an intermediary between the body and soul, and so the mental faculties are located in the ventricles of the brain. However, if this is correct, there is no reason why this organ should turn out to have an immensely complicated internal composition.
“Charles Babbage has independently suggested that many small mechanical devices could be collected into an ‘Analytical Engine,’ capable of performing activities, such as arithmetic, which are widely believed to require thought. The work of Luigi Galvani and Hermann von Helmholtz suggests that the activities of neurons are electrochemical in nature, rather than mechanical pressures as previously believed. Nonetheless, we think an analogy with Babbage’s ‘Analytical Engine’ suggests that a vastly complicated network of neurons could similarly exhibit thoughtful properties.
“We have found an enormously complicated material system located where the mind should be. The implications are shocking, and must be squarely faced. We believe that the present research offers strong experimental evidence that Benedictus Spinoza was correct, and René Descartes wrong: Mind and body are of one substance.
“In combination with the work of Charles Darwin showing how such a complicated organ could, in principle, have arisen as the result of processes not themselves intelligent, the bulk of scientific evidence now seems to indicate that intelligence is ontologically non-fundamental and has an extended origin in time. This strongly weighs against theories which assign mental entities an ontologically fundamental or causally primal status, including all religions ever invented.
“Much work remains to be done on discovering the specific identities between electrochemical interactions between neurons, and thoughts. Nonetheless, we believe our discovery offers the promise, though not yet the realization, of a full scientific account of thought. The problem may now be declared, if not solved, then solvable.”
We regret that Cajal and most of the other researchers involved on the Project are no longer available for comment.
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218
When Anthropomorphism Became Stupid
It turns out that most things in the universe don’t have minds.
This statement would have provoked incredulity among many earlier cultures. “Animism” is the usual term. They thought that trees, rocks, streams, and hills all had spirits because, hey, why not?
I mean, those lumps of flesh known as “humans” contain thoughts, so why shouldn’t the lumps of wood known as “trees”?
My muscles move at my will, and water flows through a river. Who’s to say that the river doesn’t have a will to move the water? The river overflows its banks, and floods my tribe’s gathering-place—why not think that the river was angry, since it moved its parts to hurt us? It’s what we would think when someone’s fist hit our nose.
There is no obvious reason—no reason obvious to a hunter-gatherer—why this cannot be so. It only seems like a stupid mistake if you confuse weirdness with stupidity. Naturally the belief that rivers have animating spirits seems “weird” to us, since it is not a belief of our tribe. But there is nothing obviously stupid about thinking that great lumps of moving water have spirits, just like our own lumps of moving flesh.
If the idea were obviously stupid, no one would have believed it. Just like, for the longest time, nobody believed in the obviously stupid idea that the Earth moves while seeming motionless.
Is it obvious that trees can’t think? Trees, let us not forget, are in fact our distant cousins. Go far enough back, and you have a common ancestor with your fern. If lumps of flesh can think, why not lumps of wood?
For it to be obvious that wood doesn’t think, you have to belong to a culture with microscopes. Not just any microscopes, but really good microscopes.
Aristotle thought the brain was an organ for cooling the blood. (It’s a good thing that what we believe about our brains has very little effect on their actual operation.)
Egyptians threw the brain away during the process of mummification.
Alcmaeon of Croton, a Pythagorean of the fifth century BCE, put his finger on the brain as the seat of intelligence, because he’d traced the optic nerve from the eye to the brain. Still, with the amount of evidence he had, it was only a guess.
When did the central role of the brain stop being a guess? I do not know enough history to answer this question, and probably there wasn’t any sharp dividing line. Maybe we could put it at the point where someone traced the anatomy of the nerves, and discovered that severing a nervous connection to the brain blocked movement and sensation?
Even so, that is only a mysterious spirit moving through the nerves. Who’s to say that wood and water, even if they lack the little threads found in human anatomy, might not carry the same mysterious spirit by different means?
I’ve spent some time online trying to track down the exact moment when someone noticed the vastly tangled internal structure of the brain’s neurons, and said, “Hey, I bet all this giant tangle is doing complex information-processing!” I haven’t had much luck. (It’s not Camillo Golgi—the tangledness of the circuitry was known before Golgi.) Maybe there was never a watershed moment there, either.
But the discovery of that tangledness, and Charles Darwin’s theory of natural selection, and the notion of cognition as computation, is where I would put the gradual beginning of anthropomorphism’s descent into being obviously wrong.
It’s the point where you can look at a tree, and say: “I don’t see anything in the tree’s biology that’s doing complex information-processing. Nor do I see it in the behavior, and if it’s hidden in a way that doesn’t affect the tree’s behavior, how would a selection pressure for such complex information-processing arise?”
It’s the point where you can look at a river, and say, “Water doesn’t contain patterns replicating with distant heredity and substantial variation subject to iterative selection, so how would a river come to have any pattern so complex and functionally optimized as a brain?”
It’s the point where you can look at an atom, and say: “Anger may look simple, but it’s not, and there’s no room for it to fit in something as simple as an atom—not unless there are whole universes of subparticles inside quarks; and even then, since we’ve never seen any sign of atomic anger, it wouldn’t have any effect on the high-level phenomena we know.”
It’s the point where you can look at a puppy, and say: “The puppy’s parents may push it to the ground when it does something wrong, but that doesn’t mean the puppy is doing moral reasoning. Our current theories of evolutionary psychology holds that moral reasoning arose as a response to more complex social challenges than that—in their full-fledged human form, our mora
l adaptations are the result of selection pressures over linguistic arguments about tribal politics.”
It’s the point where you can look at a rock, and say, “This lacks even the simple search trees embodied in a chess-playing program—where would it get the intentions to want to roll downhill, as Aristotle once thought?”
It is written:
Zhuangzi and Huizi were strolling along the dam of the Hao Waterfall when Zhuangzi said, “See how the minnows come out and dart around where they please! That’s what fish really enjoy!”
Huizi said, “You’re not a fish—how do you know what fish enjoy?”
Zhuangzi said, “You’re not I, so how do you know I don’t know what fish enjoy?”
Now we know.
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219
A Priori
Traditional Rationality is phrased as social rules, with violations interpretable as cheating: if you break the rules and no one else is doing so, you’re the first to defect—making you a bad, bad person. To Bayesians, the brain is an engine of accuracy: if you violate the laws of rationality, the engine doesn’t run, and this is equally true whether anyone else breaks the rules or not.
Consider the problem of Occam’s Razor, as confronted by Traditional philosophers. If two hypotheses fit the same observations equally well, why believe the simpler one is more likely to be true? You could argue that Occam’s Razor has worked in the past, and is therefore likely to continue to work in the future. But this, itself, appeals to a prediction from Occam’s Razor. “Occam’s Razor works up to October 8th, 2027 and then stops working thereafter” is more complex, but it fits the observed evidence equally well.
You could argue that Occam’s Razor is a reasonable distribution on prior probabilities. But what is a “reasonable” distribution? Why not label “reasonable” a very complicated prior distribution, which makes Occam’s Razor work in all observed tests so far, but generates exceptions in future cases?
Indeed, it seems there is no way to justify Occam’s Razor except by appealing to Occam’s Razor, making this argument unlikely to convince any judge who does not already accept Occam’s Razor. (What’s special about the words I italicized?)
If you are a philosopher whose daily work is to write papers, criticize other people’s papers, and respond to others’ criticisms of your own papers, then you may look at Occam’s Razor and shrug. Here is an end to justifying, arguing and convincing. You decide to call a truce on writing papers; if your fellow philosophers do not demand justification for your un-arguable beliefs, you will not demand justification for theirs. And as the symbol of your treaty, your white flag, you use the phrase “a priori truth.”
But to a Bayesian, in this era of cognitive science and evolutionary biology and Artificial Intelligence, saying “a priori” doesn’t explain why the brain-engine runs. If the brain has an amazing “a priori truth factory” that works to produce accurate beliefs, it makes you wonder why a thirsty hunter-gatherer can’t use the “a priori truth factory” to locate drinkable water. It makes you wonder why eyes evolved in the first place, if there are ways to produce accurate beliefs without looking at things.
James R. Newman said: “The fact that one apple added to one apple invariably gives two apples helps in the teaching of arithmetic, but has no bearing on the truth of the proposition that 1 + 1 = 2.” The Internet Encyclopedia of Philosophy defines “a priori” propositions as those knowable independently of experience. Wikipedia quotes Hume: Relations of ideas are “discoverable by the mere operation of thought, without dependence on what is anywhere existent in the universe.” You can see that 1 + 1 = 2 just by thinking about it, without looking at apples.
But in this era of neurology, one ought to be aware that thoughts are existent in the universe; they are identical to the operation of brains. Material brains, real in the universe, composed of quarks in a single unified mathematical physics whose laws draw no border between the inside and outside of your skull.
When you add 1 + 1 and get 2 by thinking, these thoughts are themselves embodied in flashes of neural patterns. In principle, we could observe, experientially, the exact same material events as they occurred within someone else’s brain. It would require some advances in computational neurobiology and brain-computer interfacing, but in principle, it could be done. You could see someone else’s engine operating materially, through material chains of cause and effect, to compute by “pure thought” that 1 + 1 = 2. How is observing this pattern in someone else’s brain any different, as a way of knowing, from observing your own brain doing the same thing? When “pure thought” tells you that 1 + 1 = 2, “independently of any experience or observation,” you are, in effect, observing your own brain as evidence.
If this seems counterintuitive, try to see minds/brains as engines—an engine that collides the neural pattern for 1 and the neural pattern for 1 and gets the neural pattern for 2. If this engine works at all, then it should have the same output if it observes (with eyes and retina) a similar brain-engine carrying out a similar collision, and copies into itself the resulting pattern. In other words, for every form of a priori knowledge obtained by “pure thought,” you are learning exactly the same thing you would learn if you saw an outside brain-engine carrying out the same pure flashes of neural activation. The engines are equivalent, the bottom-line outputs are equivalent, the belief-entanglements are the same.
There is nothing you can know “a priori,” which you could not know with equal validity by observing the chemical release of neurotransmitters within some outside brain. What do you think you are, dear reader?
This is why you can predict the result of adding 1 apple and 1 apple by imagining it first in your mind, or punch “3 × 4” into a calculator to predict the result of imagining 4 rows with 3 apples per row. You and the apple exist within a boundary-less unified physical process, and one part may echo another.
Are the sort of neural flashes that philosophers label “a priori beliefs” arbitrary? Many AI algorithms function better with “regularization” that biases the solution space toward simpler solutions. But the regularized algorithms are themselves more complex; they contain an extra line of code (or 1,000 extra lines) compared to unregularized algorithms. The human brain is biased toward simplicity, and we think more efficiently thereby. If you press the Ignore button at this point, you’re left with a complex brain that exists for no reason and works for no reason. So don’t try to tell me that “a priori” beliefs are arbitrary, because they sure aren’t generated by rolling random numbers. (What does the adjective “arbitrary” mean, anyway?)
You can’t excuse calling a proposition “a priori” by pointing out that other philosophers are having trouble justifying their propositions. If a philosopher fails to explain something, this fact cannot supply electricity to a refrigerator, nor act as a magical factory for accurate beliefs. There’s no truce, no white flag, until you understand why the engine works.
If you clear your mind of justification, of argument, then it seems obvious why Occam’s Razor works in practice: we live in a simple world, a low-entropy universe in which there are short explanations to be found. “But,” you cry, “why is the universe itself orderly?” This I do not know, but it is what I see as the next mystery to be explained. This is not the same question as “How do I argue Occam’s Razor to a hypothetical debater who has not already accepted it?”
Perhaps you cannot argue anything to a hypothetical debater who has not accepted Occam’s Razor, just as you cannot argue anything to a rock. A mind needs a certain amount of dynamic structure to be an argument-acceptor. If a mind doesn’t implement Modus Ponens, it can accept “A” and “A → B” all day long without ever producing “B.” How do you justify Modus Ponens to a mind that hasn’t accepted it? How do you argue a rock into becoming a mind?
Brains evolved from non-brainy matter by natural selection; they were not justified into existence by arguing with an ideal philosophy student of perfect emptiness. This does not make our
judgments meaningless. A brain-engine can work correctly, producing accurate beliefs, even if it was merely built—by human hands or cumulative stochastic selection pressures—rather than argued into existence. But to be satisfied by this answer, one must see rationality in terms of engines, rather than arguments.
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220
Reductive Reference
The reductionist thesis (as I formulate it) is that human minds, for reasons of efficiency, use a multi-level map in which we separately think about things like “atoms” and “quarks,” “hands” and “fingers,” or “heat” and “kinetic energy.” Reality itself, on the other hand, is single-level in the sense that it does not seem to contain atoms as separate, additional, causally efficacious entities over and above quarks.
Sadi Carnot formulated the (precursor to) the Second Law of Thermodynamics using the caloric theory of heat, in which heat was just a fluid that flowed from hot things to cold things, produced by fire, making gases expand—the effects of heat were studied separately from the science of kinetics, considerably before the reduction took place. If you’re trying to design a steam engine, the effects of all those tiny vibrations and collisions which we name “heat” can be summarized into a much simpler description than the full quantum mechanics of the quarks. Humans compute efficiently, thinking of only significant effects on goal-relevant quantities.
But reality itself does seem to use the full quantum mechanics of the quarks. I once met a fellow who thought that if you used General Relativity to compute a low-velocity problem, like an artillery shell, General Relativity would give you the wrong answer—not just a slow answer, but an experimentally wrong answer—because at low velocities, artillery shells are governed by Newtonian mechanics, not General Relativity. This is exactly how physics does not work. Reality just seems to go on crunching through General Relativity, even when it only makes a difference at the fourteenth decimal place, which a human would regard as a huge waste of computing power. Physics does it with brute force. No one has ever caught physics simplifying its calculations—or if someone did catch it, the Matrix Lords erased the memory afterward.
Rationality- From AI to Zombies Page 88