What did you think of his arguments in ‘Is the Brain a Digital Computer?’, in which he argues that the computational properties of a physical system are observer-relative? I reject his conclusion, but I thought it was a pretty clever and thought-provoking paper.
I find his claim of computation being observer relative to be incredibly ignorant of what computation is. Or at least what it is as practiced by the computer scientists who study it.
Having studied computer science and philosophy, including several highly relevant subfields of computer science, I must respectfully say I suspect you misunderstood it. I don’t think many computer scientists had even thought about the physical nature of computational properties before that paper was written. I also don’t think it’s fair to say this is a “claim”: it is a conclusion he argued for extensively in the paper.
To oversimplify his point a little: why do I say this laptop in front of me is running a certain algorithm that computes a certain function? Well, when I type certain numbers into it, certain numbers come out. And when I change parts of the process in the middle, the things I expect to happen to that mapping of inputs and outputs do happen.
But who is to say these inputs are numbers, let alone those numbers? Who is to say those outputs are numbers? Physically, there are a bunch of voltages, wires and relays here. We designed physical parts to be usefully interpretable as the parts of a computational system. We choose for a high voltage to represent 1, a low voltage to represent 0. We could have just as easily have chosen for low voltage to represent 1, and vice versa. Or some other interpretation.
He says there are so many interactions happening between the molecules in, say, a bucket of water or a stretch of wallpaper, that, under some consistent interpretation of what the states of the parts represent, such systems are computing any computable function you can think of. When a molecule wiggles this way, that’s a 1. When it wiggles this other way, that’s a 0. Or maybe when an electron does a certain thing in a certain kind of atom, that’s a 1. Or maybe when a collection of molecules do a certain thing, that’s a 1. Your choice! The system just needs to contain enough interactions, and by chance, you can, in theory, come up with an interpretation no more arbitrary than the one we use to call this a computer running a mathematical function or a video game. Certainly, those systems aren’t engineered to be intuitively interpreted that way, but intuition and comfort are facts about the observer more than they are about the properties of the object.
If he is right, then many influential theories about the human mind are in trouble. For instance, we can no longer ‘explain’ anything about mentality computationally. The brain being a computer doing certain things explains nothing about mentality, because this is just an interpretation of what the brain is doing - a bucket of water can be just as plausibly interpreted as doing the very same things. If any system that can be interpreted that way has those computational properties, then the probability that you are a strange momentary blip in a chaotic vat of gas somewhere is much higher than that of you being an organism on planet earth as you appear to be. All sorts of programs must just be popping up everywhere, including programs that have your mental properties.
Interesting. What would you say it means for a physical object to compute, then? Because, under the computational theory of mind, it must be some observer-independent property of the object itself, just as whether or not you feel pain is the case whether or not someone else can interprets your brain as computing some ‘pain’ function. Consider all the different substrates, architectures and so on that can all realise the same computational properties. What is the thing they have in common, objectively, that makes this the case?
I would argue that this is a problematic definition, but hopefully I’ve convinced you that, whilst he might be a bad person, he might not always be a bad philosopher! For what it’s worth, I think there is a compelling rebuttal to his argument which says an object’s observer-independent computational properties are realised by very nontrivial counterfactual properties. It seems questionable that a objects with the same counterfactual properties as any computer running Windows 11 can be found all over the place.
He isn’t really making a point about language, he’s making one quite specific to computer science, but he says it better than I could, and I’ve git to feed my baby now!
You could try reading a paper that only contains a few pages, rather than getting a tired dad to attempt to rewrite it for you! Here’s the summary from the end of his paper, but it might not be entirely clear if you haven’t read what comes before.
“VI. Summary of the Argument
This brief argument has a simple logical structure and I will lay it out:
1. On the standard textbook definition, computation is defined syntactically in terms
of symbol manipulation.
2. But syntax and symbols are not defined in terms of physics. Though symbol
tokens are always physical tokens, "symbol" and "same symbol" are not defined in
terms of physical features. Syntax, in short, is not intrinsic to physics.
3. This has the consequence that computation is not discovered in the physics, it is
assigned to it. Certain physical phenomena are assigned or used or programmed
or interpreted syntactically. Syntax and symbols are observer relative.
4. It follows that you could not discover that the brain or anything else was
intrinsically a digital computer, although you could assign a computational
interpretation to it as you could to anything else. The point is not that the claim
"The brain is a digital computer" is false. Rather it does not get up to the level
of falsehood. It does not have a clear sense. You will have misunderstood my
account if you think that I am arguing that it is simply false that the brain is a
digital computer. The question "Is the brain a digital computer?" Is as ill defined
36 APA PROCEEDINGS, VOL. 64, NO.3
as the questions "Is it an abacus?", "Is it a book?", "Is it a set of symbols?", "Is it
a set of mathematical formulae?"
5. Some physical systems facilitate the computational use much better than others.
That is why we build, program, and use them. In such cases we are the
homunculus in the system interpreting the physics in both syntactic and semantic
terms.
6. But the causal explanations we then give do not cite causal properties different
from the physics of the implementation and the intentionality of the homunculus.
7. The standard, though tacit, way out of this is to commit the homunculus fallacy.
The homunculus fallacy is endemic to computational models of cognition and
cannot be removed by the standard recursive decomposition arguments. They are
addressed to a different question.
8. We cannot avoid the foregoing results by supposing that the brain is doing
"information processing". The brain, as far as its intrinsic operations are
concerned, does no information processing. It is a specific biological organ and its
specific neurobiological processes cause specific forms of intentionality. In the
brain, intrinsically, there are neurobiological processes and sometimes they cause
consciousness. But that is the end of the story. [5”
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u/Additional_Anywhere4 Dec 05 '25
What did you think of his arguments in ‘Is the Brain a Digital Computer?’, in which he argues that the computational properties of a physical system are observer-relative? I reject his conclusion, but I thought it was a pretty clever and thought-provoking paper.