Re: Searle: Is the Brain a Digital Computer?

From: HARNAD Stevan (
Date: Tue Mar 20 2001 - 08:06:19 GMT

On Mon, 19 Mar 2001, Afonso Salcedo wrote:

> Harnad:
> > If it is, it certainly not at all obvious how or why it is. (Why should
> > it FEEL like something to be the reaction to a set of procedures?) And,
> > even more important, what if it's not?
> > The logic is: If the moon is nothing but a hunk of green cheese, then
> > the moon is just a dairy product. But why should I think the moon is
> > nothing but a hunk of green cheese? Just because it looks like a hunk
> > of green cheese?
> Salcedo:
> I think we can't compare the two examples: the moon/cheese and the mind, for
> one simple reason. We yet have to understand the functionality of the mind
> (be it physical or meta-physical), while we already have undeniable proof
> that the moon is not cheese.

I'm not sure what you mean by physical or "meta-physical"! But apart
from that, do you have "undeniable proof" that the mind consists of
functionality? After all, the moon does not consist of functionality,
it consists of matter. So does the brain. Whereas what we are asking
is whether intelligence/thinking/feeling are just a matter of

> Salcedo:
> It is scientifically correct to hypothesize if the mind can be described as
> a basic set of procedures, but is not to hypothesize about the moon being a
> hunk of cheese... Well, it is, but it would be a waste of time I guess...

Why is it scientifically correct to hypothesize that the mind consists
of procedures? Procedures may generate (some or all of) the mind's
PERFORMANCE CAPACITY, but above we were asking about FEELING. Feeling
is not something you do; nor is it something anyone else (but the
feeler) can observe, unlike cheese.

> Harnad:
> > He just wants to know whether or not that computer over there, whatever
> > code it is running (and whether it's an operation, simulation, or
> > representation), is really thinking, the way his brain is really
> > thinking. It's the same as asking whether whether or not something is
> > really flying, the way a plane is really flying.
> Salcedo:
> Sure, but you do need to still define your concept of thought as you need to
> define what you believe flying actually is. So you need to get into detail
> of all other sub-concepts that are in someway related to what you are
> interested on.

No, we don't define flying. We point to it. In the same way, we don't
define thinking. We point to it (the way Descartes did, and the way
everyone who thinks can do). When Newton explained moving, he did not
first DEFINE moving. He just pointed to it. And then produced the laws
of motion that provided the functional/causal explanation.

> Harnad:
> > But wouldn't exactly the same thing be true of sentences on a piece of
> > paper? Yet we would never ask ourselves whether the paper is thinking or
> > understanding. What difference does it make if the sentences are
> > implemented dynamically. The question still remains: Is that really what
> > thinking is? Is there any understanding going on there?
> Salcedo:
> Again, it's an hypothesis. A piece of paper with sentences on it is already
> fully defined and described. It can't do anything else. A computer has the
> *possibility* of evolving to the matter that it actually implements some
> process of thought, whichever that may be.

I'm afraid I couldn't follow this. Static sentences on paper are not
thoughts. Why are dynamic sentences in a computer thoughts? (I don't
understand this "possibility of evolving". And thought is what goes on
in your head when you are thinking, whatever that may be...)

> Salcedo:
> Maybe it's easier to imagine this possibility if considering advances in
> biological computing, where strand of DNA actually perform computanional
> processes as common computers do, though millions of times faster.

See the discussion of DNA and coding in my replies:

> Harnad:
> > We are not "comparing internal representations." We are asking whether or
> > not the system really thinks.
> Salcedo:
> True, but again, if we are interested in knowing if the system really thinks
> then we would have to evaluate somehow the inner workings of this, wouldn't
> we? I don't think the scientific community would accept a computer said to
> be able to think, without a thorough explanation of how it processes
> thoughts.

If we don't know whether or not thinking is computation, how can we
look at whether or not a computer "processes thoughts"? It processes
symbols; what is on trial here is whether that is thoughts/thinking.

There are other candidates for "inner workings" after all, other than
symbols and computation, for example, neuronal activity (T4).

> Harnad:
> > Kid-sib is confused upon hearing this: I understand that gravitational
> > attraction is a physical property that is "intrinsic" to physical
> > bodies. Same is true of chemical bonds. So far we have covered planets
> > and brains (gravitation, chemistry). Where does thinking and computation
> > come in?
> Salcedo:
> We don't know if we need the rest of the body to think, or if the brain can
> actually think without a body attached to it. Maybe a computer could
> function in the same way.

You have just made two leaps. Maybe a brain can think without a body,
but that has no bearing on whether a computer can think, if the brain
is not just a computer, computing.

> Salcedo:
> Maybe the physics of the hardware are irrelevant,
> but also maybe they are not. What if a computer chip can only thing if
> somehow the hardware is implemented in some biological way, like
> bio-computers?

Then thinking is not just computation, and computationalism/cognitivism
(Strong AI) is wrong.

Stevan Harnad

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