[hist-analytic] Reichenbach, Carnap, Positivism

Roger Bishop Jones rbj at rbjones.com
Wed Oct 7 12:00:07 EDT 2009

The lengthy delay in this response was caused by my
hoping to rewrite my page on "positive science" to
provide a better explanation of my reasons for thinking
little of the idea that we should be talking about the
probability of scientific theories rather than their
However, though I have done things to the page which
might help to make my position clear, I have
not yet succeeded in getting anything which I like.
(the current muddle can be found at:

On Saturday 26 September 2009 16:55:56 Baynesr at comcast.net wrote:

>"As soon as you attempt to describe the sense data you will
>introduce the possibility of error,"

>So I can be in error in describing them, say thinking the hen sense datum
> has five instead of its in fact four speckles? How about being in error in
> believing there is a datum? If you can have one sort of error, why not the
> existential?

I can't credit the idea of a hen sense datum.
It would have to be data.

In a scientific theory of perception I think you would have
to deny that the data which passes from our sense organs to
the brain have any very close correspondence with any
conscious mental process.
A sense datum would be something like the firing of a neuron,
but consciousness, of however elementary a nature, is a
macroscopic phenomenon involving very many neurons, perhaps
I think this has some connection with the way memory works
and the intimate connection of consciousness and memory.
(memory is holistic, and the things we thing we have been
conscious of are of necessity only things of which we
have memory).

The upshot is that a philosophical theory of perception
in which our knowledge of the world is mediated by
sense data which correspond closely to conscious events is
in my opinion untenable.
So the problem with dubitability of our sense data is
not just with descriptions of them, it is with consciousness.
By the time you have a conscious awareness of anything
your brain has already done a massive amount of processing
(inference) on the real data.

>"(this is like the skeptics "appearances appear")"
>Some would hold, following Plato in the Sophist, that there are no
> appearances because there is no reality; there is just the way we describe
> our experiences; "reality" need not apply.

Is that what he says there?
I thought he held that there was a "real world" (that of Platonic forms)
and that we do have opinion of the world of appearances if not
actual knowledge.

>There are a number of places where you, rightly, point out I haven't said
> enough; but these posts as you can see are very long. I think you should
> take a look at some of this stuff, time permitting.
>"I am generally not in favour of resort to talk about probability
>as a remedy for uncertainty, or the various other similar
>stratagems (such as confirmation theory)."
>Some deny there IS truth, only that there are degrees of likelihood of being
> true; or something close to this.

Well, let me explain the "Metaphysical Positivist" take on this.

It seems to me, that most scientific laws, if we are to take
them as literal claims about the universe, are false.
Typically they provide idealised models of some aspect of
reality. and like the relationship between Platonic forms
and the world of shadows, nothing in this latter corresponds
precisely to the forms.

Elementary schoolboy illustrations of this are:

1. Boyles law.
2. Hooks law.

But the phenomenon is pervasive.
I don't know any "scientific laws" which are actually literally true.

We agree that Newtonian mechanics is false but it is
much more useful than relativistic mechanics.
It is agreed that relativity theory and quantum theory
present incompatible pictures of the universe, that they
cannot both be true and are probably both false.
Einstein spent most of his life working on a unified
field theory, and now a huge amount of effort goes
in to string theory, which is the same kind of thing.
So it seems to me that physicists agree that none of
their theories is actually true.

Talking about the probability of a theory being true is not
a remedy for this "problem", because an honest assessment of
this will yield the answer -0.999 (i.e. almost certainly false)
for all scientific theories.
This problem also blights confirmation theory.

What I recommend is that we simply accept that scientific
theories provide models of aspects of reality, and should
not be expected to be literally "true".
We should then consider what information about these models
is worth having (instead of the judgement about whether
they are true).
This is probably information about the scope of applicability
of the model. its accuracy and reliability (in various
areas of application).
In a positivistic vein, I believe that scientists should
evaluate theories in such terms and simply publish in details
the results of their analysis and the details of the observations
on which their assessments are based.

I believe Popper recognised an issue for falsificationism here
(presumably that scientific theories are too easily falsifiable).
He distinguished between falsification and rejection (so
the scientist is supposed to be focused on falsifying his
theories but if he succeeds that does mean he abandons the
Popper, I understand. tried to work out some notion of
"verisimilitude" which is a measure of how close a theory
comes to truth, but I think his efforts in this are not
highly regarded, and deductivists continue to seek some
numerical measure along these lines (David Miller has put
one forward recently).

There does seem to be a lot of interest in finding numbers
which we can attach to theories which tell us how good they
are, and they all seem unconvincing to me.

So, metaphysical positivism is pragmatic in this area.
I advocate asking the question,

  "what is this theory good for"

and providing long and complicated answers supported by
experimental data showing accuracy and reliability of the
theory in different circumstances.

>A cynical comment on my part on Hume: If Hume is right, there are a few
> conventions having to do with arithemetic or vacuous tautologies at best,
> and then there is the psychology of belief. There is no real need for
> philosophy, unless we think of it as a way of describing psychological
> facts of experience. An overstatement? Just a little, perhaps.

This was not Hume's view.
Hume did not consider mathematics to be trivial.

Hume did think of philosophy as a branch of empirical science.
That's why his grand opus was "A Treatise of Human Nature".
His manner of reconciling this with his scepticism is not impressive.

>> This will effect
>> the logic of science. Truth values will be infinite between 0 and 1. There
>> won't be two truth values. Much of this was supported by the Heisenberg
>> business.

Hume was quite explicit in rejecting the idea that scepticism about
matters of fact can be fixed by talk about probabilities.
He not only claimed that we do not have certain knowledge of
matters of fact, but also that we do not have certain knowledge
of the probability of any factual proposition.

>What I mean by a "theory of ontology" is a theory as to how to answer the
> question "What is there?" in the sense that epistemology answers the
> question: "How do I know?" (in a broad sense of 'how', including what is
> knowledge etc
>In the Aufbau, Carnap is pretty much a phenomenalist. I think you are
> relying too much on Schilpp, but I may be wrong.

I invariably talk about Carnap's mature view unless I explicitly talk
about earlier ones.
I don't doubt that the Aufbau is phenomenalistic, but I do doubt
that Carnap was a dogmatic phenomenalist even at that time.

In fact, if we are to believe Carnap's own words in the Schilpp
volume, he was not a dogmatic phenomenalist even at the time he
wrote the Aufbau.
His section on pseudo-problems (I.II.5 p44) opens as follows:

   "During the time I was writing the Logischer Aufbau,
   I arrived more and more at a neutral attitude with respect
   to the language forms used by the various philosophical
   schools, e.g  the phenomenalistic language about sense data
   and the realistic language about perceptible things and events
   in the so-called external world."

>If mathematics is a bunch of tautologies and explanations are of the sort
> Carnap accepts (the sort of thing Hempel had in mind, i.e. deductive
> nomological explanations etc) then the question is what is the basis for
> thinking these empty sentences relate to the world? Reichenbach's answer is
> that this is owing to their use in making predictions. Otherwise they say
> nothing of value. I'm not sure what you mean by a possible world. I never
> been to one.

That's a rather anti-metaphysical view you seem to be taking there.
However, I think you are broadly correct in saying that scientific
explanations relate to the world through their utility in enabling
predictions to be made.  However, I have lost your point here.

>"Someone is surely a materialist only if he asserts that only matter
> exists,"
>Yes, and a physicalist who believes what is physical is material is a
> physicalist just the same, and conversely a materialist who believes that
> matter is physical is a materialist just the same. No problem here.
> Language has little to do with it.

But Carnap was neither a phenomenalist, nor a physicalist, nor a
theoreticist, he was a pragmatist in accepting the legitimacy of
linguistic forms, and in took a pragmatic stance on the
"external" metaphysical questions which might be thought
presupposed by use of these languages.
So I would not myself call him a materialist and suspect that
he would not call himself a materialist.

>A language containing theoretical terms is "reducible" through operational
> definition to the physicalist language, so physical language and
> theoretical language differ only in the descriptive constants being in the
> one case terms that refer to unobservables. So there is no difference in
> languages, especially once the protocol language, via Neurath, is reduced
> to a physical language.

I don't recognise this as Carnap's position.
Carnap's principle of tolerance was not predicated on reducibility
of languages to phenomenalistic language.
It is true that he was interested in the relationship between non
phenomenalistic and phenomenalistic language, but that does not mean
that he affirmed the possibility of a reduction (his conception of
the kind of relationship he was looking for evolved, but I don't
think it was ever part of a criterion of acceptability, on which
he was pragmatic).

As for the "unified language" stuff, that was more an attack
on the idea that there are fundamental differences between the
physical sciences and the social sciences than a program for
phenomenalistic reduction.

Roger Jones

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