Ingvar, (01)
I learned a lot from Quine, but I don't follow him all the way.
In particular, Quine was adamantly against modal logic, possible
worlds, and a distinction between intensions and extensions. (02)
JFS>> It happens that English has no tenseless verb forms.
>> In predicate calculus, you could write:
>>
>> ~(Ex)(rose(x) & blue(x)).
>>
>> This statement has no reference to any time or place.
>> In English, it is possible to make a statement without
>> reference to place, but not to time. (03)
IJ> And isn't this the reason why Quine introduced his notion
> of 'eternal sentence'? And propositions expressed by
> eternal sentences cannot change truth-values, can they? (04)
Quine didn't adopt any notion of 'proposition', 'sentence
meaning', or 'use of sentence meaning'. My motivation for
getting into this business was to develop a semantics for
natural languages. And that requires some notion of context,
modality, and inten(s/t)ionality. (05)
In a Kripke style of modal logic, there may be true statements
(even "always true" statements) in one possible world that are
not true in other possible worlds. That doesn't imply that
their truth values "change", but that they may have different,
yet unchanging truth values in different worlds. (06)
I sympathize with Quine's opposition to possible worlds, which I
prefer to replace with Dunn's semantics of laws and facts. That
provides the equivalent of possible worlds for the purpose of
supporting modal logic, but it avoids the dubious ontology of
fictitious worlds. In its place, you get an ontology of abstract
entities, such as laws, propositions, and contexts, which I am
more willing to accept. But then you get propositions with
different truth values in different contexts. (07)
IJ> Are you denying the old truth: 'same meaning, same reference'?
> To me, this truth implies 'same proposition, same aboutness',
> which you are denying. (08)
What I would call into question is the word 'same'. Following is
another of my favorite quotations from Whitehead, _Modes of Thought_: (09)
In logical reasoning, which proceeds by use of the variable,
there are always two tacit presuppositions -- one is that the
definite symbols of composition can retain the same meaning
as the reasoning elaborates novel compositions. The other
presupposition is that this self-identity of each variable can
be preserved when the variable is replaced by some definite
instance.... The baby in the cradle and the grown man in middle
age are in some senses identical and in other senses diverse.
Is the train of argument in its conclusions substantiated by
the identity or vitiated by the diversity? (p. 146) (010)
If you take a position that is both realist and fallibilist, you
have to admit that reference, as well as truth, is fallible. (011)
My approach is to develop a two-valued logic, which supports
contexts (and metalanguage about the contexts) in which propositions
may have different truth values in different contexts -- and which
allows metalevel reasoning about those truth values in a containing
context. The metalevel can talk about probabilities or even a
continuous range of fuzziness or truthlikeness -- but it certainly
does not require any such assumptions. (012)
I discussed those ideas in my KR book and developed them more
fully in the following two papers: (013)
http://www.jfsowa.com/pubs/laws.htm
Laws, Facts, and Contexts (014)
http://www.jfsowa.com/pubs/worlds.pdf
Worlds, Models, and Descriptions (015)
The worlds.pdf paper, which was published more recently, may be
a better introduction. The laws.htm paper has more detail about
the models. In those papers, I did not mention Common Logic or
IKL, but I believe that IKL provides the mechanisms I need to
define the contexts and metalevels I assume. (016)
John (017)
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