Re: Propositionsphayes@cs.uiuc.edu (Pat Hayes)
Date: Thu, 12 May 1994 12:08:13 -0500
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To: sowa <email@example.com>
From: firstname.lastname@example.org (Pat Hayes)
Subject: Re: Propositions
John, a few quick comments.
>These are OK. I prefer the definition I gave, which is quite simple
>and allows you to have as fine-grained or coarse-grained a definition
>of "proposition" as you like: namely, a proposition is defined as an
>equivalence class of sentences in some formal language.
The problem with this 'definition' is that it is vacuous. It has the
diplomatic advantage of applying to almost anything. If 'propositions'
(whatever they are) can be expressed by sentences in any way at all, then
the equivalence relation on sentences is that they express the same
proposition. Voila! But we havnt learned anything more about propositions.
And de re propositions can't be expressed syntactically, in any case.
>>> And another famous source of complication comes from de re propositions. Is
>>> this a proposition: the person standing behind you is female? If not, why
>>> not: if so, how could it possibly be expressed in a formalism?
>> On a fine-grained approach, what proposition the sentence "The person
>> standing behind you is female" expresses is going to depend on context
>> and on your intentions as the speaker. If you are using the
>> description as a mere tag to pick out a certain individual (so that
>> the correctness of the description doesn't really matter), then (on
>> the "Russellian" view, at least) you are expressing a singular
>> proposition containing the person in question as a constituent (what
>> you're calling a de re proposition, I take it), the proposition itself
>> the result of a certain sort of predication operator that takes an
>> n-place relation and n individuals as arguments.
>My response to Pat is somewhat different from Chris's, which I don't
>really disagree with.
I think you must. An equivalence class of sentences definitely does not
contain a person as a constituent. Chris' reply nicely illustrates the kind
of complication that classical accounts of proposition get into. De re
propositions, whatever they are, are not even remotely syntactic in nature.
But I would say that if your formal language
>is FOL, you can't say "The person standing behind you is female"
>or "This sentence is false" because you have no way to express context
>dependent or indexical terms in FOL. If your formal language is CGs,
>which do support indexicals, then I would say that the equivalence
>classes are not defined over any CGs which contain indexicals.
>That means that you must first resolve the indexicals to some
>contextually defined individual before you can apply the equivalence
>axioms. For Pat's example, that would be to resolve "you" to some
>individual, say Bill, and then to resolve "the person standing
>behind Bill" to some other individual, say Mary. The result is
>that you have the proposition containing the sentence "Mary is female."
That kind of analysis won't work. Maybe neither of us know her name, but
the proposition is still adequately expressed by the sentence. I agree that
some notion of 'context' seems to be needed, but such contexts can include
anonymous physical objects, or maybe even anonymous or undifferentiated
physical or sensory phenomena (as in "Thats a beautiful sunset" or even
"What the hell was that?" used to refer to an unusual environmental state
such as an earth tremor.)
(To clarify: I am not arguing that such information cannot be adequately
encoded in sentences of some formalism. What is at stake here is the notion
of 'proposition'. Semantics of descriptive formalisms can be given without
ever introducing the murky notion of proposition.)
>>> The finest minds in Western civilisation havn't come to a consensus
>>> on this in hundreds of years. We should be very sceptical of a
>>> committee of even the *very best* computer scientists claiming it
>>> has a 'standard'.
>> Agreed, it would be sheer hubris to propose *the* standard account of
>> propositions. ....
>I agree with both Pat and Chris, but I also believe that we need
>a standard. ...
Er...sorry? Could you go over that again?
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