Ingvar Johansson wrote:
> Waclaw Kusnierczyk schrieb:
>> Yes. I think John has conflated a theory's being true and a theory's
>> being empirically adequate.
> I doubt this very much. He has at least not given me this impression. He
> is a fallibilist who often refers to Peirce. (01)
quite possible. i said 'i think', to stress that this was only my
(subjective) opinion. (02)
> Being a fallibilist means
> to accept that a theory may be empiricially adequate for a time without
> being completely true. I think what (reading vQ:s mail) might be
> pedagogically missing in Peirce and Sowa is a concept advertised by
> another fallibilist, Karl Popper. He verbalizes it using three different
> expressions: ‘truthlikeness’, ‘verisimilitude’, and ‘approximation to
> truth’. Theories are not just either true or false; truth can take
> degrees. And very very much tells in favor of the view that most
> empirically adequate theories have a rather high degree of truthlikeness. (03)
i am not sure how much to like the 'partially true' and 'truth can take
degrees' parts. (04)
clearly, if we think of a theory as of a set of statements, the theory
is partially true if there is a subset of it with every statement being
true. (every theory is partially true, since every theory includes the
empty theory, which is vacuously true.) (05)
clearly, partial-truthness can have degrees, or be characterized by the
fraction of the theory that is true wrt. to the whole theory. but
'truth can take degrees' sounds oddly to me. a theory that is properly
partially true (the maximal part or subset of it that is completely true
-- or, simply, true -- is a proper part or subset of the theory) is not
true. parts of it are true, but the whole is not. (06)
i would thus say that theories are either true or false, tertium non
datur. the question in individual cases is how much of the theory is
true (or false). this is mostly a terminological issue, i think, but i
sue to think of truth as having no degrees. (07)
>> a theory may perfectly fit the data and
>> allow for usable predictions, even if it is wrong about the nature of
>> the phenomena addressed.
>> I thus support the statement that there *is* a difference between a
>> theory's being correct and its being accurate, and consequentially, that
>> there is a difference (beyond the obvious syntactic one) between saying
>> that a theory is true and that a theory is accurate.
>> If you could prove that a theory necessarily makes correct predictions
>> in every possible case, you could claim that the theory is true (but I
>> am not still convinced this would be correct). You can't (not in
>> empirical sciences, perhaps in mathematics); theories are induced or
>> abduced from partial data (data about only some part of the reality).
>> They are not tested on every conceivable input, since what is the set of
>> all conceivable inputs is only another theory.
>>> By the same token, if someone offers a theory that does not give correct
>>> predictions or that relies upon what I suspect are fanciful premises,
>>> i.e., airplanes fly because the motors attract fairies that carry the
>>> plane aloft, I can ignore that theory because it is less useful than
>>> some other theory. Such as calculating the thrust needed by a jet engine
>>> to propel the next generation of jet aircraft. I don't ever have to
>>> reach the issue of "truth" but can rely upon theories that I find useful
>>> for some particular task.
>>>> Newtonian mechanics, in fact, is such a theory. During the past
>>>> century, physicists have discovered phenomena of relativity and
>>>> quantum mechanics, for which Newtonian mechanics makes incorrect
>>>> predictions. However, for macroscopic phenomena at nonrelativistic
>>>> speeds (i.e., for cars and airplanes) Newtonian mechanics is a true
>>>> description of reality. I trust my life to Newtonian mechanics
>>>> whenever I drive a car or fly in a plane.
>>>>> A friend of mine sent me the following example:
>>>>> There is an elementary model in electrical engineering, called
>>>>> the "4-terminal network". The thing is a closed ebony container,
>>>>> with an input, an input return, an output, and an output return.
>>>>> The student is given a set of inputs and outputs, and asked to make
>>>>> the simplest thing that he can which could be substituted for the
>>>>> actual contents of the container. The problem of what is _actually_
>>>>> inside the container is dismissed as impossible.
>>>> That is an excellent example.
>>>> If anyone defines a theory (i.e., a set of axioms) that correctly
>>>> predict the output for every conceivable input, then I would say
>>>> that the theory is a true description of the behavior of that box.
>>> First, "every conceivable input" isn't really possible. Testing is
>>> always with a finite set of inputs.
>>> Second, I would say that a theory (set of axioms) that correctly
>>> predicts all the inputs we have tried is simply accurate. That is it
>>> agrees with the inputs and predicted outputs.
>>> Calling a theory "true" or "part of truth" doesn't make it any more or
>>> less accurate. The aether theory was at one time thought to be "true"
>>> but that did not save it from being superceded.
>>> I suppose that is what I am missing. What claim is it, beyond accuracy
>>> (agreement of theory with observations), that you want to make by saying
>>> something is "part of the truth?" (If any claim at all. I may simply be
>>> over-reading your statement to imply more than it is actually saying.)
>>> Hope you are having a great day!
Wacek Kusnierczyk (010)
Department of Information and Computer Science (IDI)
Norwegian University of Science and Technology (NTNU)
Sem Saelandsv. 7-9
tel. 0047 73591875
fax 0047 73594466
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