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In his 1980 article “Minds, Brains and Programs” John Searle wrote:

” Of course the brain is a digital computer. Since everything is a digital computer, brains are too. The point is that the brain’s causal capacity to produce intentionality cannot consist in its instantiating a computer program, since for any program you like it is possible for something to instantiate that program and still not have any mental states.

Ten years after he wrote (or spake, it was the Presidential Address delivered before the Sixty-fourth Annual Pacific Division Meeting of the American Philosophical Association in Los Angeles):

” 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 as the questions “Is it an abacus?”, “Is it a book?”, “Is it a set of symbols?”, “Is it a set of mathematical formula?”

Apparently Searle changed his opinion in these ten years, since the statements appear to be directly mutually contradictory. Regarding that aspect I mailed Searle, but he didn't answer. A typical SO reader may think I'm unrealistic in expecting an answer, and indeed in my experience, limited to two cases though, philosophers do not answer critique or admit to errors, but e.g. in my own field of C++ programming the top people such as Bjarne Stroustrup and Andrew Koenig are more than willing to discuss things, admit errors (and collect them in errata lists), and so on, and that's also for a few cases been my experience in the field of physics (e.g. I once pointed out a problem with the description of something in Scientific American's "expert answers" column and they put John Baez on it who just fixed it). So I don't think I was unrealistic. But no answer so far.

Hence I'm asking here:

  • Did he change his opinion, or is it just that a negation of the meaningless is still meaningless, thus not really contradictory?

  • What on Earth does or did it mean that “the brain is a digital computer”. Literally it's just nonsense, and that interpretation is compatible with both of Searle's statements. I find it difficult to think of a more meaningful interpretation that is also compatible with both.

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    It seems to me he's saying the same thing both times. There is a sense in which everything is a digital computer, and in that sense, the brain is a digital computer too. There is also a sense in which everything is a book, and in that sense, the brain is a book too. But these are not terribly useful observations. If we want to ask whether the brain is a digital computer (or a book or an abacus) in some "deeper" sense, we quickly descend into meaninglessness. This seems to me to have been clearly Searle's point, both times. – WillO May 13 '15 at 16:32
  • PS --- In my experience, pretty much any serious workers in any discipline is glad to have his errors pointed out, but few serious workers in any discipline are likely to take the time to respond to random emails from people who would rather play "gotcha" games than take a few minutes to digest the material they claim to have read. – WillO May 13 '15 at 16:34
  • @WillO: I'm sorry I had to flag your 2nd comment for mod attention (the 1st comment is just meaningless to me, but the 2nd is ad hominem). Hopefully it will be deleted so that people won't judge you on the basis of a single silly personal attack. Assuming that it is the only one, of course. – Cheers and hth. - Alf May 13 '15 at 16:52
  • Re @WillO 's 1st comment above, he maintains that Searle was arguing against a meaningless idea that brains are books or computers or whatever. But as far as I know nobody had argued in favor of such, and Searle certainly did not cite or refer to any such claim in his 1980 article. Thus, WillO is making an unsubstantiated claim that Searle originally was using irony with reference to some other's claim that only Searle knew about, i.e. WillO is claiming that Searle was assuming a telepathic reader. Which in my humble opinion is worse than the assumption of nonsense. – Cheers and hth. - Alf May 13 '15 at 17:05
  • I too find that philosophers do not like to admit their arguments are wrong; while one would expect philosophers to be able to make and communicate clear arguments, they seldom ever convince each other about anything; sadly, I do not find it very different from a multitude of family members discussing politics in vain ad infinitum; much too often they employ convoluted technical jargon to create unintelligible arguments which are practically impossible to refute; philosophers of mind are no exception. – nir May 13 '15 at 19:46
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In reverse order:

  • "What on Earth does or did it mean that “the brain is a digital computer”. Literally it's just nonsense": Obviously the brain doesn't use binary code or run assembler, it uses neurons and analogue signals. The use of the word digital here is very misleading. What is meant here is that the brain is functionally equivalent to a digital computer in the largest sense of the word, i.e. the brain is equivalent to a Turing Machine. This is to say that the brain is capable of the same finite and discrete computations that a Turing Machine is capable of, even if it goes about it in a different way. This is essentially a variation on the Church-Turing-Deutsch thesis , that any physical process (including brain processes) is computable by a Universal Turing Machine. The key words here are finite and discrete. Remember that Turing's original intention wasn't to describe what an electronic calculating machine can do, but to describe the process of performing a calculation in general.

  • I don't think the two statements are contradictory. What he is saying in the first one is that the statement "the brain is a digital computer" while accurate, doesn't fully describe the brain. To use another example, the statement "The brain is a lump of organic matter" is accurate as well, but doesn't describe the brain's functioning either. In the second statement, he is further elaborating, saying that just as the brain can be identified with a digital computer (or a lump of organic matter), it can also be identified with abacuses and books and so, but none of these are accurate since they fail to convey what the brain really does.

His main target here is the computational theory of the mind. He is attacking the idea that the brain is equivalent to a Turing machine, by saying that things like intention and meaning cannot be represented by a Turing machine no matter how powerful - I disagree with him, Hofstadter gives a very good account of how intentionality and meaning can arise in formal symbol processing systems in GEB. I also find Searle's Chinese room example to be completely wrong, but that topic is out of scope.

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  • Just re " Church-Turing-Deutsch thesis" from 1985, I find that an unfortunate mixture of mathematics (Church-Turing thesis) with vacuous philosophy, namely Deutsch's observation that reality might, and he was clear that it was a might, be in principle computable. I understand what you mean though, that Searle was just a little bit communication-challenged and really meant to say "Of course the brain can be simulated by a digital computer, since...". But then his 1990 statement is that it's nonsense, or as he wrote "it does not get up to the level of falsehood. It does not have a clear sense". – Cheers and hth. - Alf May 13 '15 at 17:51

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