[hist-analytic] Reichenbach, Carnap, Positivism

Roger Bishop Jones rbj at rbjones.com
Fri Nov 6 03:24:15 EST 2009

This is a bit of rave from the grave, I wrote most of it ages ago, filed it in 
drafts, and only just got back to it.
Really i wanted to make some more substantial observations about prevalent 
misconstruals of the extent of Carnap's metaphysics, but it will have to wait 
for another time.

On Monday 12 October 2009 Steve Bayne wrote:
> "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."
> On the theory we are talking about the idea is not that sense data mediate
>  anything. Sense data ARE the world.

I thought we were talking about the philosophies of Carnap and
Reichenbach, and I don't believe that either of them subscribed to that
kind of metaphysics. Furthermore, I was explicitly talking about
theories of perception, which seems to me more relevant to the aufbau
than metaphysical ontology, since we know from Carnap's writings that he
did not intend the Aufbau to be understood as metaphysics.

> That is, given a strict empiricist
>  methodology on this theory, or one version of it (say Russell in Mysticism
>  and Logic), there are only sense data.

I don't see that even a strict empiricism commits you to that position.
Conceivably a strict positivism might, but neither Carnap nor
Reichenbach were strict positivists in that sense.

> It is the world. That is the theory.
>  Now I could play devil's advocate and, I think, present a good case for 
>  view.

Feel free.
I, and I believe Carnap and Reichenbach would say that there is not, and
could not be, a shred of evidence in favour of that theory.

> It is, basically, Hume's view as well.

I should be interested to have references to substantiate that.
Though Hume is an extreme sceptic about our knowledge of an external
world, I have not myself seen anything in his writings which amounted to
a denial that there is such a world.

> There are impressions and
>  ideas. Impressions can be thought of as sense-data (on one "traditional"
>  construal of sense data); and ideas are only less vivacious reminders of
>  those impressions. If you are a strict Humean the closest thing to 
>  you will ever get are impressions.

Maybe you can't get any closer, but that doesn't mean that material
objects don't exist.

> "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."
> You've misunderstood. It may be my fault. Let me clarify. The sophist, as
>  opposed to the philosopher who can view the Forms, denies the existence of
>  images, because he uses images in his craft of persuasion. If he admits to
>  them, he admits being a deceiver. That is Plato's theory throughout his
>  entire career. No exceptions.

You are surely not telling me that Plato was a sophist!?

In any case, I don't see how that bears upon my point, though we have
now lost to much context to know what the real issue is here.

> "What I recommend is that we simply accept that scientific
> theories provide models of aspects of reality"
> But now how do we distinguish "models" and "theories" and "laws"? Typically
>  "laws" in a collective can be identified with a theory. I'm not keen on
>  this, but this is a popular view. But then how does a model differ from a
>  theory? Of course they differ, but on your view how?

A theory (which I agree might encompass a collection laws) is a claim
about reality which, provided its meaning is clear, will be either true
or false.

A model is not a claim about reality, and so is not the kind of thing
which can be true or false.
Having constructed a model, one may then wish to say something about its
merits, but in this one can be more refined than a bald assertion of
truth or falsity.
Thus we might say of Newtonian mechanics, when presented as a model of
certain aspects of the behaviour of physical objects, that it has a
certain degree of accuracy when applied to certain classes of systems,
and we would be able in such a claim to stipulate bounds on the
velocities involved.

> "Popper, I understand. tried to work out some notion of
> "verisimilitude" which is a measure of how close a theory
> comes to truth,"
> Not sure if this, rightly, characterizes Popper. I haven't done much with 
>  theory of probability.

It wasn't offered as a characterisation.

>  I think there are problems with it, but I haven't
>  take a close look. But just one question: How can I know how close to truth
>  I am if I don't know where the truth is? Is it like hide the thimble, a 
>  I played in early youth. The thing is hidden and the hidder can tell you
>  when you are getting close by saying 'hot' or 'you're getting cold'. But 
>  hidder has to know where it is; so, someone has to know. Elaborate, if you
>  care to, on how I can know how close a theory comes to truth without 
>  what the truth is.

I agree that there are problems with the notion of verisimilitude.
Talk of models is an alternative to talk about verisimilitude, and works 
without our needing to have any wholly satisfactory (or "true") theory.

Roger Jones

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