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Re: Working without being ambushed by Ambiguity (was: issue-57 background reading for F2F (short required reading)

From: Pat Hayes <phayes@ihmc.us>
Date: Thu, 25 Oct 2012 09:48:05 -0500
Cc: Tim Berners-Lee <timbl@w3.org>, Graham Klyne <GK@ninebynine.org>, David Booth <david@dbooth.org>, "www-tag@w3.org List" <www-tag@w3.org>
Message-Id: <75D34E6D-5F55-4E06-BEED-D4235317F922@ihmc.us>
To: Larry Masinter <masinter@adobe.com>

On Oct 24, 2012, at 3:47 PM, Larry Masinter wrote:

>>> Rather than putting those off as an afterthought to be worked out later, while
>> failing to get a handle on a theory of meaning without them, they need to be
>> central.
>> All of these rest on the basic notions of a name or identifier referring to
>> something, and the truth of a proposition expressed by some sentence (or
>> "contentful structure" of some kind.)
> I don't think it's necessary to rest the layer cake on "referring to something".

Here's why, in a nutshell. All of the other stuff you are talking about only makes sense at the level where we have propositions in the mix. Persistence is a proposition staying true (or staying false, of course) over time. Belief is belief in the truth of a proposition. Trust is trusting that when you utter a proposition, I am inclined to believe that it is true. Unless we have actual propositions, none of this makes sense. (If all you do is make meaningless noises at me, what does it mean to even say that I believe you or trust you?)(**) And the truth-values of sentences expressing propositions rests on what the names in those sentences refer to. Change the referents, you change the truth-value. 

> Yes, I understand that's the model you're using, where a name or identifier refers to "something" independent of the person, time, or context involved in uttering, considering, or encountering the name or identifier.   I'm suggesting a different model, where any notion of "refer" is always situated by context.

Hmm, I wonder if you do understand it, in fact. Model theory doesn't claim independence from person, time or context, or indeed anything else. What it does do, is require that if these (or other) things are part of your theory of truth, then you have to say *how* they affect truth. There are more model-theoretic formalizations of reasoning in time, or reasoning in contexts, than you can shake a stick at. 

The basic idea is not that referents are fixed in some absolute sense, but that the truth of an utterance depends upon how referents are assigned. Change the referents, you (might) change the truth-value, and hence the content of an assertion (asserts = claims to be true). So for example ambiguity can give rise to misunderstandings because the proposition the speaker intends to assert is not the proposition that the reader actually gets, because they apply different interpretation constraints upon the names in the utterance. But until we have *in our theory* an adequate account of how this kind of thing happens (which model theory provides) we will never manage to even get started. 

The problem with your idea, "where any notion of "refer" is always situated by context" is that if you take it seriously, it becomes very hard to explain how *any* communication can take place, since if the "context" of the speaking is different from that of the hearing, then the signal's meaning might change arbitrarily during transmission. (Another problem, by the way, is making it clear just what a "context" is. I have been to a number of conferences and workshops devoted to context reasoning and context logics, and have noticed that almost every speaker has a different notion of "context". The word "context" is highly contextual.)

(BTW, it is kind of ironic that you say here that my theory requires rigid referents, when I have been waging a war of attrition against TimBL and the TAG now for years, wanting them to *stop* claiming that URIs identify uniquely, precisely because model theory rules this possibility out, and shows how ambiguity - or vagueness, if you prefer - is inevitable.)

FWIW, I agree with you about contexts. I have a fairly detailed proposal to make RDF into a context logic, which could be done without affecting existing deployment and would resolve, or at any rate ease, a number of contentious issues, including http-range-14 and the best way to interpret SPARQL datastores. But it hasnt got any traction partly because people find model theoretic thinking too difficult, apparently. You can see it at http://www.slideshare.net/PatHayes/rdf-with-contexts (meat starts at slide 10)

>> We need to get the naming and the sentential structure clear before we can begin to make sense of ideas like provenance, belief or trust.
> I disagree that doing so is a "need". I understand that is the approach you're taking, and it isn't working.

Its working pretty well. It handles all the inference-making on the Web, for example. 

> I don't think the model which starts with reference and adds provenance, belief, and trust, is adequate for the kind of analysis needed.
> I'm looking for a model that starts with reference being a personal individual act, and communication is based on correlation through turst.

If reference is a personal individual act, how do I communicate my references to you? It is exactly the communication that we need to analyze. And if communication is correlation, then correlation *of what*? And how is such correlation achieved? Presumably, by sending messages of some kind. If you pursue this line of thought, I bet you will quite quickly re-invent Tarski's theory of truth. Communication is achieving alignment of beliefs by transmitting sentences expressing propositions. That is exactly what model theory is about. 

>>> For example, the notion of "meaning" is tied completely to persistence.... a
>> use of a URI is "cool" to the extent that its effect on recipients (its "meaning")
>> doesn't change (over time or the range of recipients).
>> Wrong on several counts.
> I put "meaning" in quotes because I wasn't using the term in a way I thought you would agree with. Rather than argue about it, just try it out as a definition instead, change "is tied" to "should be tied".

Well, first, why don't you tell me what *you* mean by "meaning" ? Start with a simple example like "Snow is white." :-)

>> Everest is a mountain, what I mean is something about a place in Nepal, and
>> mountains. I have no idea what a recipient is going to use this for or what effect
>> it might have on them, and that has nothing to do with what I mean.
> Humpty Dumpty used words without any idea of what a recipient might use it for or what effect it might have on them. 

Humpty Dumpty said that words mean what he wanted them to mean, because he was the master. That sounds to me more like your idea that reference is a purely private matter.

> I think you're doing yourself a disservice by claiming you have _no_ idea. You don't have a complete and accurate idea. When you want to say something, you say enough, with enough hyperlinks and other reference material, to help the poor reader.

But suppose that I have no idea who the reader is, or what use they are going to make of my words? All I can presume is, they understand English (or RDF, etc.). And surely that is the normal case on the Web. The hyperlinks and reference materials help the reader better understand what propositions I am trying to say, sure. But as to *why* the reader might be interested in this stuff, or *how* it might influence their behavior, I neither know nor care. We communicate at the level of transmitting propositions, but it doesn't get more intimate than that.

>> (And this is
>> just as well, since on the Web I cannot *possibly* know what effect it might
>> have on them.) 
> Of course, you can't possibly know EVERTHING about what will happen. But surely it is the writer's obligation to consider the reader.

But not to know so much about the reader that one is setting out to sculpt their behavior, or still less that this sculpting is the meaning of ones words. 

>> Second, meaning does not depend upon persistence.
> Insofar as communication travels the speed of light or lower, there is a time delay between the writer writing and the reader reading. Sometimes it's minutes, sometimes days, weeks, months, years, decades, centuries.   Over many of those time scales, the web changes. Insofar as you intend future readers to understand what you write, you use terms that will retain some quality. Perhaps you don't mind if a blogger changes the style of their blog, as long as the content is still there. The things you don't mind changing are irrelevant to meaning, the things you mind if they change are highly correlated with meaning of the link.

All that means is, you try to keep your meaning expressed in a way that will last. For example, its not a good idea to use tenses without putting a date on your writing so that readers can figure out when you are talking about. But all of this rests on the fact that your writing is expressing propositions. If you were writing music, for example, none of this would apply. You would just write the notes on the stave, and that would be that. No dates, no trust, no content (other than the music itself), and no real communication; all because, no propositions.

>> If my
>> uncool URI changes its reference every week, then each week's meaning is
>> perfectly clear (we can suppose) even though persistence is lacking.
> See time delay above.

I wasnt talking about that issue. My point was, that even when there is no persistence, there can still be perfectly clear meaning. So the latter can't depend upon the former. 

>> Weekly
>> magazines might be good examples. Persistence might in fact be better defined
>> in terms of reference and meaning rather than the other way around: for
>> example, RDF and SPARQL have spend some time defining notions of
>> equivalence which allow referents to change 'harmlessly' precisely because the
>> *meaning* doesnt change.
> Exactly, I just think you are looking in the wrong end of the telescope. Turn it around. Start with persistence, and tell me what you see about meaning.

Nothing much, for the reason above. 

>>> As long as we talk about statements (triples) or terms (uris) having
>> disembodied meaning or fail to take into account trust, error and malice, we're
>> not making progress....  and wasting time.
>> Until we do get "disembodied" meaning clear, we will never get out of the can
>> of worms far enough to even get started on these harder problems. I agree
>> they aren't afterthoughts, but they are thoughts that must come after.
> If you start with what you think is the beginning, then yes, other thoughts must come after. I'm suggesting a different starting point, since the one you've been using isn't working.

Well, as I say, I think it is working. Progress is slow, but these are complicated issues which havnt yet caught the attention of most of the relevant specialists. Model theoretic semantics has a long history and has been applied to a very wide range of kinds of language and communication. At the very least, it makes sense to adapt it to the Web rather than throw it away and try to re-invent the wheel.


(**) OK, there is a notion of trust where what I trust is that you will *do* some predictable thing in response to input from me. In this sense I trust my cat to look at me when I call his name, and my OS to open a menu when I click on the desktop background. And this doesnt reat upon communication of propositions. But I don't think that the sense of trust involved in Web thinking is this simplistic.


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Received on Thursday, 25 October 2012 14:48:42 GMT

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