# Re: (biassed) summary of the argument so far.

phayes@cs.uiuc.edu
```Message-id: <199306041928.AA27380@dante.cs.uiuc.edu>
Date: Fri, 4 Jun 1993 14:32:49 +0000
To: interlingua@ISI.EDU, sowa@turing.pacss.binghamton.edu,
sowa <sowa@turing.pacss.binghamton.edu>
From: phayes@cs.uiuc.edu
X-Sender: phayes@dante.cs.uiuc.edu
Subject: Re:  (biassed) summary of the argument so far.
Cc: cg@cs.umn.edu, cmenzel@kbssun1.tamu.edu
```
```John-

We seem to be nearly at a state of mutual comprehension, if not

>.... pure mathematics isn't about anything
>until you make a decision to apply it to something. To me, this
>distinction between pure & applied mathematics seems so fundamental
>and so elegant that I can't see why anyone would object to it.

Of course, this is almost tautologous.  I would just say 'mathematics'
rather than 'pure mathematics', however: you usage makes it sound like
there are two kinds of maths, which is pedagogically useful but not
really correct. But I suspect we agree here, in fact.

Our difference lies in what we think it is to 'apply' mathematics. You
seem to take this to involve far more than I take it to. All one needs
to do, in order to apply some mathematical ideas, in my view, is to
ensure that the area of application satisfies the assumptions made by
those ideas (which for set, and hence model, theory, is not much). You
seem to take it to involve far more than this.

>Please excuse me for bringing it up again, but you made the comment
>that tensor calculus was "applied mathematics".

That was before I fully understood your usage, which I now have

>But I said that it
>is just as pure as set theory.  Originally, the subject was developed
>for the purpose of applying it to stresses and strains in solid objects
>(whence the name "tensor").  But then the same mathematical structure
>was applied to relativity.  If you make the distinction, tensor calculus
>is pure and it has two very different major applications.  But if you
>don't make the distinction, it becomes very difficult to talk separately
>about the mathematical operations and the domain of application.

This distinction is exactly that between use and mention. In applying
a piece of matrhematics one is using it as a language to talk about
something or other. Since this way of speaking is so convenient we
often speak as though there really were abstract things that the
'pure' mathematics is about: 'things' like the Klein group, say (as
opposed to something which
displays that group structure, like the set of rotations and
reflections of a rectangle.)  Whether or not one wishes to allow such
abstractions in the universe is to some extent a matter of taste, but
the use/mention distinction keeps track of the difference between the
math itself and what the math is supposed to be about.

>
>> ... I find your insistence that
>> lexical representations must refer only via a computational
>> 'simalcrum' of something real, which itself is only related
>> vaguely to the actual world, to be alarmingly confusing on
>> precisely this issue....
>
>Fine, we seem to agree about the distinction between lexical and
>nonlexical items.  In an earlier note, I believe that you were
>also willing to accept the meaning triangle, which puts concepts
>in the middle between words and things.  Is that correct?
>
>If you don't accept the meaning triangle, then I can understand
>your objecting to my computational surrogates.

Well, the meaning triangle is fine when the LHS is taken to mean
language, ie human, natural language. As I said in earlier notes,
then the middle of it becomes the represented knowledge, in whatever
form it might be encoded. For example, all of CYC's knowledge base
would be attached to the center node of that triangle, not the
'language' node.

>But if you do accept the meaning triangle as a reasonable hypothesis
>about intervening mental states in human use of language, I cannot
>understand why you would object to an intervening level of surrogates
>in a computational system that is used to relate a language (natural
>or artificial) to the world.

That suggests where we disagree. The use of 'language' to refer both
to natural language (which is used by humans to communicate) and
(hypothesised) representational languages (which are used by agents
to represent and infer) is little more than a pun, in my view, and

The meaning triangle says nothing about surrogates. It is only a way
of saying that (natural) language refers to the world via thoughts
or concepts, which seems like an insightful point. It says nothing
at all about how such concepts should be implemented or whether there
should be two 'levels' of mental representation.

I chiefly object to the notion that invoking a level of 'surrogates'
is somehow necessary or compulsory in order to apply model theory to
the analysis of logical representations, ie that logical representations
can refer only to other computational structures. This seems wrong on
two points. First, if we replace it with a notion of 'abstract' or
views on the nature of pure mathematics. But even then, there would
seem to be no justification for thinking that such things would (or
even could) take the form of actual computational or mental structures.
This just seems obviously wrong. For example, I believe that there
are hundreds of billions of stars. Does this mean that I must have
a surrogate universe with hundreds of billions of surrogate stars

>And I am not sure about your use of the word "vaguely" in your
>comment above.  Did you mean that in a deprecating sense as some
>sort of criticism of my point?

Yes, I confess, although it does reflect the fact that I don't
understand quite what this relationship is supposed to amount to,
and don't believe you have explained it clearly. Again I wnat to
make a distinction which you seem to be blurring(?), between
an analogical representation which is 'similar' to what it
represents (like, say, a floor plan of a room), and something
like a detailed description of what it represents, which a
database would be. But this is a minor point.
...
>The notion of surrogate gives me a very clear way of distinguishing
>the perceived reality (either in my head or in a computer simulation)
>from the actual reality, which may in fact be quite different.

This is easy to distinguish. What you mean by 'perceived reality'
is something like 'the way the world would (or might) be if my
perceptions were correct', I presume? That is a model of my
(perception-governed) representation of it.

Just a side comment: there is only one reality, of course, so
'the perceived reality' is only a metaphorical usage. I hope we
agree on this.

>To me, it seems to be a very natural way of talking about things.
>I really don't understand why you object to it so strenuously.
>Are you objecting because you want to distinguish some abstract
>theory of meaning from some computational implementation?

Just say 'theory of meaning', and the answer is yes. Of course I
distinguish the *theory* of meaning from anything computational:
again, that is a use/mention distinction, like the distinction
between the theory of internal combustion and a V-6 Ford engine.
The theory of meaning isnt the kind of thing one would (usually)
seek to implement, its a theory of what such implemented
things might mean.

>  When I see the phrase "there exists"
>in a mathematical textbook, I interpret it in a metaphorical
>sense, similar to the way I would interpret a novel or a myth.

I agree with this general idea, although I am quite willing to
countenance a more platonic approach. (And agree with Quine that
it is very hard to avoid allowing some abstract entities into
ones ontology, such as the integers. Even the intuitionists
allowed the integers.) Part of the utility of set (and hence
model) theory is precisely that it is completely agnostic on
this issue.

I would distinguish a philosophical position on this stuff from
a pragmatic one. I lean towards nominalism, but also admit that
actual working mathematics requires one to appear to adopt a
much more platonist view. The strenousness of my objections to
your messages has been motivated more by my strong belief that
it is necessary to maintain this freedom to be ontologically
promiscuous than by my disagreement with your particular views.

To insist that logical representations must refer only
via some kind of computational surrogate seems to me to be an
unwarranted intrusion of a very particular philosophical stance on
semantic, and even computational, practice. It seems to me to
be mistaken (surrogate galaxies??), confusing (use/mention,
deductive roles of databases, distinctions in earlier messages),
and unnecessary (model theory relates sentences to things
perfectly well).

But you know, the real reason for pursuing this so relentlessly
has been the sheer pleasure of trying to discover what on earth
you are saying, and Ive had to adopt some debating tricks to
dig this out. I feel like I understand you now, so thanks for
the edification (but don't go saying that I agree with you,
mind...:-)

Best wishes

Pat Hayes

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