Re: The meaning of "meaning"Pat Hayes <email@example.com>
Date: Mon, 10 Feb 1992 15:37:29 PST
From: Pat Hayes <firstname.lastname@example.org>
Subject: Re: The meaning of "meaning"
Cc: srkb@ISI.EDU, interlingua@ISI.EDU, email@example.com,
Pat Hayes <firstname.lastname@example.org>
In-reply-to: Your message of Fri, 7 Feb 92 14:38:40 EST
Again I will abbreviate to try to keep messages to a reasonable length.
>Since I believe this discussion touches on some of the central problems
>in KR, I would like to continue it in the open forums (with apologies
>o people who prefer skinny mailbox lists).
I agree. I don't want to have to make that many copies of a message again. So,
listen in, folks, you are getting to hear this whether you like it or not.
By the way, I could quote messages of congratulation from people who are tired
of trying to explain to an NL person why NL is beside the real point. So we
both have troops, lets take that as given.
>The linguist Dwight Bollinger coined a famous slogan "Every difference
>makes a difference." He made that point in answer to Chomsky's claim
>that certain transformations (e.g. active-passive) preserved "meaning".
>Bollinger agreed that such transformations preserve the truth value of
>the sentence, but he claimed that there is much more to meaning than
>just truth value. One such component is presupposition and focus, where
>you say "This is what I assume we are talking about" and "This is what I
>want to add to the knowledge base in your head."
>I regard semantics as the study of meaning. The denotation of sentence
>in a model-theoretic sense is a very important component of meaning, but
>I agree with Bollinger in claiming that there is a lot more to meaning.
But this is all beside the point of our argument. You are talking about natural
language. I agree there is a lot more to the meaning of natural language than
can be expressed in any kind of model theory applied to surface syntax. There
are speech acts and innuendo and sarcasm and God knows what going on there when
people communicate with each other. In the right context, a simple "uh-huh?"
can carry a mess of meaning. I am not talking about natural langauge, but about
a hypothesised mental representation langague, a Language of Thought. And I
dont think the LofT is much like a natural language. (Arguments why are too
long to summaridse here, but one can be explained succinctly. If we agree with
the Stanford philosophers that NL is essentially indexical in nature, then
LofT, since it is the vehicle for memory, cannot be similarly constructed or
our memories would have the same indexical quality and they would all seem to
be about 'now'.) By simply talking about 'meaning' you are blurring this
>Dixon, being a linguist, uses the term "semantics" in a broad sense.
I can't let that go by. He uses it in exactly the same narrow sense that you
use it, ie as referring to the meaning of natural languages. But enough of this
pointscoring. I agree that the study of NL is a valuable source of semantic
intuitions, perhaps the most valuable one we have; and I agree wholeheartedly
that studies which span many langauges are likely to be more interesting than
ones which are tied rigidly to the idiosyncracies of one, especially one as
historically peculiar as English. To agree with this, however, is to regard
languages as a source of evidence, not as a rigid framework on my methodology.
( I can't help noting, for example, that if we take Bollinger's dictum
seriously, then EVERY difference Dixon has found in surface sytax in ANY
language must somehow be mirrored in a distinction in the semantic language.)
>From a logician's point of view, his book might be considered a study
>in the underlying ontologies of various natural languages.
I havent yet seen Dixon's book (thanks for the reference), but that sounds
>In that context, you would definitely want to translate "a red ball"
>into an existential. The negation would come from the word "never",
>which would govern the context containing that existential.
Well, thats one way to do it. Another might be to make this mean something
which would be directly rendered into English as 'all the owning experiences I
have had have not had red-ball as an accurate description of their object',
which doesn't directly existentially quantify over any balls.
> Predicate calculus is based
>on C. S. Peirce's first effort to represent full FOL (his notation
>of 1883). By 1897, he had scrapped that notation in favor of his
>existential graphs, which he called "The logic of the future".
>I prefer Peirce's revised, improved logic to his first attempt.
Transatlantic cultural piracy in full swing!! Predicate calculus is based on
the work of Frege as adopted and enriched by Russell and Whitehead in Principia
Mathematica. However, your point holds since Frege used a graphical notation.
If one really likes graphs, that is fine. But most of the work that has been
done has been done in the linear notation, and the (almost pre)history is not
really relevant. Not a big issue as far as I am concerned, provided of course
one does not try to patent a notation as familiar as semantic graphs.
>> I am really at a loss to see what the difference in meaning between these
>> noun phrases could possibly be. I believe you have hallucinated it.
>The question of how to represent colors, shapes, etc., is an extremely
>serious issue for databases and knowledge bases. You will find all kinds
>of examples in the literature where some people write "red(x)" and others
Again you miss my point. Of course ontological issues are important and need
work. But why should the distinction be so closely tied to the surface syntax
of English sentence construction? You assume this as a given; I am calling it
into question and asking you why I should believe it, and you still have not
answered my query. The difference between the noun phrases is only like that
between the two PC atoms under the assumption that the syntax of the
referential langauge mirrors that of surface English very directly, which of
course is the issue in question.
> I would say that both forms are truth-functionally
>equivalent, but that "red(x)" uses a first-order expression, while
>"color(x,red)" uses a second-order expression. The second-order form
>makes it easier to quantify over colors and store them in a database.
They both look first-order to me. The second is second-order only if a color is
taken to be a property, which does not seem very plausible. For example, a red
can be bright, and a brightness ( in particular, that of a red ) can be
dazzling. So you can't stop at second-order, it seems, once you start away from
the safety of first-order...
>The reason for the current confusion is that there are no clear
>guidelines for deciding how to choose the predicates.
I agree. Well, "A reason for..."
>What I have
>been trying to do is to state guidelines for choosing predicates based
>on linguistic criteria and then use transformations based on lambda
>calculus for translating one choice of predicates into another.
No complaints. In fact, I wish you well in this enterprise, which follows in a
fine tradition in linguistic theory. I don't think you will ultimately succeed,
and I think I know why. And still less do I see why this has much to do with
the KIF effort. Why should a selection of ontological primitives for, say, an
engineering system to help designers of electric motors, have much to do with
categories suggested by the syntax of English?
>What I was recommending is the ATTR (attribute) relation for linking
>an entity to a concept derived from an adjective and the CHRC
>(characteristic) relation for linking an entity to a second-order type
>like COLOR, SHAPE, etc. Then you can do all the transformations with
>one lambda definition that relates CHRC to the ATTR plus KIND relations.
>Of course, you also need a dictionary that says which words in English
>are second-order terms, etc. Nothing is ever free, but at least there
>is a way to put some order in the process.
Well, I don't want to knock your work, but I can't help noting that what you
seem be offering is a distinction between two kinds of properties or attributes
which is motivated by syntactic quirks of English, and an apparatus to
translate from one to another. Suppose I suggest that of the properties a thing
might have, some are to be called 'A' and some are 'B'. I will give you a large
dictionary of which is which and an apparatus to translate one into the other,
ie any assertion using 'A' prediactes can be translated into a 'B' form and
vice versa. The difference has no operational or semantic significance
whatever. Would you buy it from me?
>Yes, I keep repeating again and again that it has no truth-functional
>difference. But I also keep showing that it has operational significance
>in how you do knowledge engineering, how you choose your axioms, how
>you translate one choice of predicates into another, etc.
AHA!! Now I understand what you are claiming better. Your claim is that these
distinctions somehow guide the process of knowledge engineering. OK, thats an
interesting claim, but I don't believe it. Its not clear to me how it has much
affect on, for example, my choice of ontologies. Should I think of events as
objects with a spatiotemporal shape (and if so, what kind(s) of shape) or as
functions from situation to situation? I have heard it argued convincingly that
English is losing its future tense, and vernacular French has completely lost
it: should I abandon reasoning about the future? You see why I find syntax
less than an ideal guide. There are many difficult ontological issues, thats
for sure, but English doesnt seem to offer me much usefu lguidance when things
And by the way, I havn't seen anything that tells us how to write our axioms. I
guess I think that K. engineering is a very difficult process and one which
can't be neatly handled, or even usefully guided, by any simple correspondence
to surface syntax. Whenever I get to a hard problem of Krepresentation, English
syntax doesnt seem to help me very much.
>> ....But I
>> wouldnt talk about reifying verbs here: 'verb' is a syntactic category, not
>> a semantic one.
>Yes, I agree. When I am using the formal apparatus of conceptual graphs,
>I say "Verbs should be represented by concepts, not relations."
Clearly we are still talking past one another....
>Yes, but it is also an issue in ontology and lexicography, since most
>type hierarchies that one finds implicit in NL dictionaries are very
>bushy, but not very deep -- the top is usually not very far away.
Yes, an interesting point and one that I take to be a little more evidence on
my side, since all serious attemptsto build a large K. base, especially one
with a 'commonsense' feel to it, seem to have developed much deeper
heirarchies. A deeper point is to query how you know the shape of the NL
dictionary tree? Maybe if one came up with more accurate translations of the
meanings of the words and phrases, the heirarchy would spread in a vertical
> We might
>agree that describing a house in polar coordinates or rectangular coordinates
>makes no difference in meaning. But just try giving your local contractor
>a set of house plans in polar coordinates.
This misses a whole lot of points. First, the ridicule comes from using the
difference in a communication. But that is exactly my point: there is an
essential difference between the situation of communication (over a narrow
channel) between intelligent people, and that of being an internal vehicle for
storage, retrieval and inference.
But anyway, the importance of the difference here is obviously the difficulty
of computing the relevant pieces of information in one case. (I am extending my
house right now, so am unusually familiar with the need to know the lengths of
things parallel to the walls.) But the differences you have been drawing our
attention to, which are settled by the application of a single
lambda-expression, no recursion, etc., are computationally piffling.
And i think McCarthy's dictum, that we should concentrate on the basic
structure of the representation and leave computational niceties for later, is
still a good one.
>... again I would say that our differences result from what we
>consider important for knowledge engineering.
> ...But two people who are using the same KR language can't share
>a KB unless they choose the same types and relations or have some rules
>for translating one choice into another.
I agree, of course. And now I am puzzled as to how you have translated our
disagreement into apparently you arguing that ontology is an important issue
and me ( presumably) that it isn't? We were disagreeing about whether the
knowledge representation languge should, as a matter of doctrine, have a
representational distinction corresponding to every surface distinction of
English. You say, essential: I say, unnecessary and potentially misleading.
>Natural languages are a goldmine of information about the implicit
>ontologies that generations of people have found useful for representing
>everything that is important in their lives.
No argument: but that is not to say that we need to be mechanically driven by
syntax-governed rules (or even much concerned with syntax, I believe.)
>Just because some naive
>prospectors may have settled on iron pyrites is no reason why trained
>prospectors should stop looking for gold.
Now, I wonder where one gets the right kind of training?
>>> Nothing that can be computed or stored on a computer is ever infinite.
>> Look, we must be misunderstanding one another. My point was only that the
>> domains of models are typically not computational entities. .... I think we
>>agree here, in fact.
>We agree pretty much in principle, but I would say evaluating denotations
>in terms of models is of immense economic importance. ... So I would want to
>keep it high on the list of goals and requirements.
John, you seem to be shifting around. On the one hand, we were concerned with
what I took to be a scientific issue to do with the representation of (models
of) human knowledge. Now we are concerned with the detailed pragmatics of
engineering. Both are worthy of care, but they may not push in the same
directions. In particular, most 'common sense' reasoning is not concerned with
models which can be made into databases.
>If it helps to end on a point of agreement, I'll stop here.
So will I.
PS John, did you ever have the feeling you were being watched?