**From:** Salcedo Afonso (*afonso@mac.com*)

**Date:** Fri May 25 2001 - 02:00:31 BST

**Next message:**Basto Jorge: "Re: Dennett: Making Conscious Robots"**Previous message:**Henderson Ian: "Re: Babbage/Menabrea: Analytical Engine"**Maybe in reply to:**Sparks Simon: "Harnad: Cognition Isn't Computation"**Next in thread:**Wright Alistair: "Re: Harnad: Cognition Isn't Computation"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ] [ attachment ]

*> HARNAD:
*

*> So although it is usually left unstated, it is still a criterial, if
*

*> not a definitional property of computation that the symbol
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*> manipulations must be semantically interpretable -- and not just
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*> locally, but globally: All the interpretations of the symbols and
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*> manipulations must square systematically with one another, as they do
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*> in arithmetic, at the level of the individual symbols, the formulas,
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*> and the strings of formulas. It must all make systematic sense, in
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*> whole and in part (Fodor & Pylyshyn 1988).
*

Salcedo:

For a more complete definition of what computation is one has to note

that even if all the symbol manipulations occur on arbitrarily chosen

symbols that don't have any form of meaning by themselves, it must still

make systematic sense when looking at the symbol system.

But what is exactly meant by a symbol being systematically

interpretable? Well, a '+' is only a plus sign because we were taught

that it represents addition. It might have several different meanings,

but it still makes sense to whoever sees it.

*> HARNAD:
*

*> We usually invoke this image to contemplate the likelihood of [monkeys]
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*> their typing a passage from Shakespeare by chance.
*

Salcedo:

There is also now the theory that we already have millions of monkeys

typing away on computers and Usenet is not yet a Shakespeare work of

art...

*> HARNAD:
*

*> A computer, then, will be the physical implementation of a symbol
*

*> system -- a dynamical system whose states and state-sequences are the
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*> interpretable objects (whereas in a static formal symbol system the
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*> objects are, say, just scratches on paper). A Universal Turing Machine
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*> is an abstract idealization of the class of implementations of symbol
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*> systems; a digital computer is a concrete physical realization. I think
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*> a wall, for example, is only the implementation of a trivial
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*> computation, and hence if the nontrivial/trivial distinction can be
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*> formally worked out, a wall can be excluded from the class of computers
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*> (or included only as a trivial computer).
*

Salcedo:

Harnad says that trivial systems are those where you can swap the

interpretations of the symbols and still come out with a meaningful

semantics.

I cannot understand how a wall can be considered the implementation of a

trivial computation. A wall is not performing anything at all. What

arbitrary set of symbols can you change on the "wall" symbol system?

What semantics? Does it even have semantics? I don't think this example

is important for the discussion being fought here: the difference

between trivial and non-trivial computation and that we are actually

only interested in non-trivial computation (is this an example of strong

CCTP?).

*> HARNAD:
*

*> A cat on a mat can be interpreted as meaning a cat on the mat, with the
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*> cat being the symbol for cat, the mat for mat, and the spatial
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*> juxtaposition of them the symbol for being on. Why is this not
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*> computation? Because the shapes of the symbols are not arbitrary in
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*> relation to what they are interpretable as meaning, indeed they are
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*> precisely what they are interpretable as meaning.
*

(...)

*> Completely different symbol-shapes could be substituted for the ones
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*> used, yet if the system was indeed performing a computation, it would
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*> continue to be performing the same computation if the new shapes were
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*> manipulated on the basis of the same syntactic rules.
*

Salcedo:

I still have some trouble understanding this. Considering that the

symbols "cat", "being on" and "mat" only exist in english and are only

associated with their real-world meanings if one knows english. Now

considering three completely symbol-shapes in some other language, that

somehow if the symbols in "cat being on mat" were substituted by these

new symbols in order to mean exactly the same thing, would this now be

computing?

Anyway, a "cat" is only a cat because the evolution of the language said

it to be so, so it is intrinsic to us. If for a Martian a "cat" means

"1", "being on" means "+" and "mat" meant "2", then would this be

computation for him but not for us? Surely, "true" computation is

computation universally.

**Next message:**Basto Jorge: "Re: Dennett: Making Conscious Robots"**Previous message:**Henderson Ian: "Re: Babbage/Menabrea: Analytical Engine"**Maybe in reply to:**Sparks Simon: "Harnad: Cognition Isn't Computation"**Next in thread:**Wright Alistair: "Re: Harnad: Cognition Isn't Computation"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ] [ attachment ]

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