Dear Pat,

It seems to me that we agree on many matters.

So let me identify areas of agreement to build upon.

I have been repeatedly saying that experimenters describe their
experiments to one another using words---such as "nose", "leaf',
"pointer", "mirror", and "the number 8"---that a child
can understand. Perhaps they should say "Looks to me like a nose", 
"looks to me like a leaf", "looks to me like a pointer pointing to 
the number `8' on the dial", etc. to emphasize that at the level
of description I am concerned with the experimenter is referring to a
visual appearance that he has learned to associated with a word, not with 
any some deeper understanding of some theory. I have emphasized 
(with Bohr) that this common everyday language gets refined by 
scientists and technicians, so that they can set up and report 
the results of more refined experiments.

You seem basically to agree. You say:
"However, I still fail to see what this has to do with our argument.
The fact that the science language emerged from everyday language.." 

So, we do seem to agree on this this point, though you fail to see its
crucial role in my position.

You complete the above sentence with: "...is hardly reason to say that 
it must not refer to the mental."  But I have not said that ALL experiments
"must not refer to the mental". I am focusing on a particular subset of all
scientific experiments that are described basically in terms of what
experimenters can see, and can talk about by means of conventional
words that refer to certain named spacetime forms that they 
are able, by virtue of their indoctrination, to recognize visually.

Later you say: 
"Sorry to be repetitive, but I still don't seem to have made my point
clear to you. Try the other word: `leaves'. Classical physics says nothing
of `leaves', so it can't predict anything about them until one has an
account of how leaves are made up of the stuff which classical physics
DOES talk about - particles and fields, say. You say that `no extra 
vocabulary is involved in the description of the observed fact', but 
this is clearly false if the observation is to somehow refer to a `leaf'.
Your technician can announce that the color is that of patch # 752
which is what is usually called `green' , but how does he tell everyone 
its the leaf that has this color? Must he say something like, 
`assemblage of fields and particles number 568, 258, 984, 674, 231'
is green? (In fact, I think this is just generally false. This idea of
physicist's technicians simply reporting pure observations of where energy
impinges just does not fit the way things are actually done. Even the 
purest observation is imbued with the non-physicists language: `pointer'
and `dial' aren't concepts in classical physics either; and the observations
are often of such things as the shape of a graph, or the presence of a
precipitate.)"

The parenthetical remark again seems to confirm that we are in 
agreement on these matters: you are saying what I have been stressing
over and over, that the observers are reporting what they are seeing:
`pointers', `dials', `shape of a graph', `the presence of a precipitate'
using everyday language, perhaps refined, to be sure, but still expressed 
in terms of these various named spacetime forms, AND DEFINITELY NOT 
EXPRESSED IN TERMS OF PARTICLES AND FIELDS. That is exactly what I 
have been stressing, and exactly what Bohr stressed.

And the part before the parenthesis is also saying the same thing:
the experimenters do NOT use the language of particles and fields to
describe the leaf. The leaf is what a child recognizes as a leaf;
or if some more detailed description is needed for some reason, such
as how it looks under a microscope, or what sort a tree or plant 
it was taken from, then a certain technical refinement of everyday
language is needed. But still, for the particular class of experiments
that I am considering, the experimenters are describing basically certain 
named shapes in space, perhaps evolving in time.


I said: " And the fact that the light lands where it does is something
that can be reported in everyday language by a child."

You replied:" But surely you don't claim that the mechanism of color production
by complex molecules can be explained in everyday language by a child
(do you??)"  

No! All I said about the child was that he could recognize and describe the
place on the dial (e.g., between the numbers `8' and `9') where the light 
landed. This is just the same point as before: the observations are described 
in everyday language, perhaps refined as needed. So we DO seem to agree on
that key point.

You say: "This point of yours (Bohr's) about `everyday' language seems
irrelevant to me, but also seems quite wrong. Everyday language most 
decidedly does not contain, say, partial differential equations."

We agree! The child does not need differential equations to be able to 
say that he picked a `leaf' off of an `apple tree',and that the light 
spot reflected off of this leaf lies between the numbers `8'and `9' 
on the dial: everyday language, refined, is used too tell others what 
he has done and what he has seen. This is not the only experiment 
where this everyday kind of language is sufficient.

You then say, about everyday language: " On the otherhand, it DOES
contain a whole lot of first-person language which we use to refer to
our mental states and dispositions". True!

Then you say: " But nothing whatever follows, then about excluding
the first person-mental talk from science." Absolutely true!
My ambition is precisely to incorporate such talk coherently into
science!

You say:" this is so obvious that I am puzzled by your emphasis
on Bohr's point,"

Bohr's point was not about excluding anything from ALL of science.
Bohr was talking about a certain kind of experimental evidence, and
how we describe it.

I think that our disagreement stems from the fact that the issue has not been
clearly set forth: that you are arguing against some idea from your 
past, not against what I am claiming.

So let me state what I am claiming.

According to the precepts of classical physics there is a physical
world that contains all of the objects that we see about us, plus air
and some other things that we do not normally see. That physical world
consists of tiny particles and fields: all objects such as leaves, and
pointers, and dials that scientists can point to, and visually share,
are asserted by the theory to be built from them. These particle and 
fields are asserted by the theory to evolve according to deterministic 
laws that completely fix all positions and velocities of all particles 
(and the values and rates of change of all fields) at all times t later 
than any chosen time T in terms of the values of the quantities before 
that time T. The "complete classical physical description of nature" 
consists of the description of the particle and field values mentioned 
above FOR ALL TIMES from the infinite past to the infinite future: 
it is a complete history.

It is generally believed that our conscious experiences are not an explicit
part of this complete classical physical description in terms of particles
and fields that physicists deal with, which nevertheless is dynamically 
complete. Nor does the existence or content of human experience appear to 
be deducible from (logically entailed by) the complete classical physical 
description plus the laws and principles that constitute classical physical 
theory. However, these experiences are generally believed, by those who
believe classical physical to be adequate in this context, to be fixed 
by the complete classical physical description of nature PLUS some 
extra psycho-physical rules that hold true in nature.

I myself agree that neither the existence nor content of human 
consciousness is logically deducible from the complete classical 
physical description of nature plus the laws and principles that 
constitute classical physical theory. [I shall give (once again)
my reasons for this belief at the end of the letter.]

But I believe that a *better* understanding of the brain/mind system will
show conscious experience to be a physically integral part of that system,
not the epiphenomenal sideshow that classical physics says it is.
[I also think quantum theory provides an ideal framework for
accomodating this integration, but that issue is not the one before 
us here.]

Let us now return to the child who picks the leaf from the apple tree, 
and puts it in the optical device, and announces that the light reflected 
off of the leaf ends up between the marks `8' and `9' on the dial.

[]Or one can consider a slightly older child, slightly trained, announcing
that the `cell wall' of the `cell' he was examining under the microscope
was disintegrating, where these words mean only that he has witnessed
a certain visual sequence.]

In my previous message,  I said of a similar experiment:
No extra "theory" is involved here. And nothing depends on what "I know" 
now or did not know (read "the child" in place of me) about plant biology.
If the classical theory were correct it would necessarily, by itself, entail
where the light reflected off of any leaf would go if it were passed through
a prism. This is simply because if the classical conception of nature were
correct, then the complete classical physics description would specify where
every bit of energy and matter is at every instant of time, and that would
specify in particular where the light that is deflected throught the prism
would land on the screen.

You responded:
"It would make that prediction only if the experimental circumstances 
you and I have been describing as `the light reflecting off... the leaf'
were somehow to be translatable into the language which it (classical 
physics) uses. Until that is done, any assertion about leaves is logically
disconnected from it: it can predict NOTHING about it, no matter how 
detailed and total was its prediction of where all the the matter and 
energy were going to go. Suppose such a prediction is done, and written 
in God's Notebook: all the positions of all the particles and energy 
fields for the entire future. Now what follows about leaves? NOTHING 
AT ALL, until one has some way to unpack the idea of `leaf' into the 
language used in this celestiallogbook. I think you are simple 
taking this unpacking for granted, but it isn't so easy to do!

" For leaves, of course, we now know enough to be able to imagine 
such a translation of leaf-language into physics-language, at least 
in principle. One takes all the stuff of the leaf, specifies the 
locations of all the cells and the parts that make them up, and the 
parts that make those up, etc., until one (in principle) comes up with
a description of all the atoms which together make up all the matter 
contained in the leaf... then classical physics claims that it can,
in principle, ... predict what will happen next.  (Right?) But 
notice that this conception is only feasible because we know now how 
leaves are made up from smaller pieces of stuff. A  few hundred years 
ago, a perfectly reasonable answer to this might have been that there 
was no such reduction: that leaves, being living things, were endowed 
with a special vitalist property which removed the from the realm of 
of the purely physical. This seems ludicrous now that we know about
biochemistr, but *all that extra knowledge is needed to provide the 
connection*. Without it we just can't `find' the leaves in all those 
particles and fields."

This is your central argument. How does it relate to my thesis
that the complete classical physics description does not entail 
the existence of consciousness?

Well, at the point you seemed to be accepting my main thesis about
lack of entailment of consciousness but were arguing that similiar
gaps occur also the physical sciences: i.e., that consciousness is 
not greatly different in this respect from the subject matters of 
the physical sciences.
 
But I was arguing that if one accepts classical mechanics 
then the complete classical physics description DOES entail
the observable facts of, for example, physical biology, which are
defined to be the facts about biological systems that are visible 
to, and recognizable by, properly trained technicians, and that are 
communicable by them to the scientific community. 

To illustrate this I took "The case of the green leaf", which you had
raised as an example of your argument.  
 
But you now agree that the complete classical physics description
(which by the way obviates any need to "predict", because it
gives the entire physical history of the world) does entail
that the child would see that the light reflected off of the leaf 
(that he picked off of the apple tree) does end up at the location
entailed by the complete classical physics description of nature.

You suggest that this result is a consequences of detailed biological
knowledge acquired over the past few hundred years; and that it 
would *not* follow if the vitalist assumption were adopted. But the 
assumption, here, is that concepts of classical mechanics do hold.
This is all that is needed. For it rules out the vitalist assumption that
the  classical principles are insufficient to determine everything; and it 
also entails that the final conclusion of your reductive analysis of the 
leaf is valid, even in the absence of a detailed biological theory of the
constitution of leaves. You said: "this conception is only feasible 
because we know how leaves are made up of smaller pieces of stuff".
But the classical conception by itself already asserts that the leaf 
is made up of smaller parts, and also that the complete classical physics 
description says every about the full history of all of these parts; 
and also everything about these parts interact with everything else, 
including light. So it can certainly do the job that you said the 
biological theory of the leaf could do. On the other hand, the details of
biological theory is far from complete, even now, and is certainly not
known to be completely causal. So the complete classical physical
description *can* do the required job, but the biological theory 
probably cannot. 

The key point here is that (following Bohr) I define the biological 
terms used to describe the observations on the biological
system in terms of the names that trained technicians use to describe
to others what they have done and what seen. Since the topic under 
discussion is `what is entailed by the complete classical physics 
description,' I describe the biological system (leaf or cell) by 
following this physics description up to the point where the trained 
observer sees the recognizable form, leaf or cell, and I use this 
recognition to define the biological object in question, in the context
of physical biology. These physics-based facts, "recognized" by trained 
observers, are communicated by word and symbol into the realm of 
experiences of biologists, who may or may not form other opinions or 
other theories about them. These other opinions and theories *are* more 
disconnected from the classical physics foundation, because they may 
make no reference at all to the particles and fields of the classical 
physical theory. 

The point of all this is to show how the physical facts that are the 
basis of the physical sciences are entailed by the complete
classical physics description of nature, without encountering any
gap of the kind encountered in trying to tie consciousness to brain
activity. 

The lack of a large gap in the physical cases is a consequence 
(as spelled out in earlier letters) of the following fact: in those cases
what are being compared---in making the connection of `the physical world' 
(as it is conceived of in classical physical theory) to `our
relevant experiences of that physical world' ---are essentially `conceptions 
of the world constructed from generalizations of our visual experiences' 
to `our direct visual experiences themselves'.

There is no comparable common denominator for comparing the classical 
conceptualization of an active brain (as a complex spacetime activity 
in  one' skull)  with the sensations of redness and sadness, or
perplexity and hunger.

I turn now to your questions.

You say:
"LOOK, here is the issue. Can there be an explanatory reduction of the realm
of experience to classical physics? Well, it depends on whether a
translation of the experience-language into that of the physics-language
can be found. If one can, then we can (in principle) provide such a
reduction, closing the current explantory gap; but if not, we can't. Can
such a translation ever be found? Well, it depends on whether or not an
explanatory reduction exists,...etc. We are going around in a circle. You
insist that this explanatory gap must exist. It certainly exists NOW, but I
see no reason why this must reflect anything except our own ignorance.
Classical physics predicts that it can explain everything, ultimately, in
terms of particles and fields. Does that include experience? I don't know:
if it does, it can do it, and if it can't then it can't. How does ANYTHING
you have said bear on this decision?"

Yes! You talk here about "translations". But the issue is entailment!
One may or may not be able to dream up some translation between
languages. But that does not allow the facts in one description to 
ENTAIL the facts of the other description. The question is only what can
be logically deduced simply from the the facts of the classical physics 
description. I thought that you had already granted that there was no way 
to *logically deduce* from the physical description of the brain in terms 
of particles and fields the fact that "redness" or "intolerance" is 
actually experienced, and experienced in just the way that it is 
experienced. 


I(HPS) said:
>Now an important point must be made here. If there is a gap
>in the normal classical laws of physics that allows the
>particle-and-fields to do whatever they actually do without
>experience being present then zombies would be possible, within
>the framework of the classical theory, regardless of whether or
>not `other gaps' exist.

PH said:
"Let me give you some other examples of LOGICAL possibilites within the
framework of classical theory which become  impossible only when a
sufficiently detailed 'connecting theory' is provided.

1. Squareoids. A squareoid is a planetery system in which some of the
planets move in square orbits rather than elliptical ones.
2. Bombzies. A bombzie is somthing of the opposit of a zombie: it has a
fully-fledged rich internal life of conscious experience, but it's neurones
never fire at all.
3. Flying pigs made of concrete and butterfly wings.

Get the idea? All you need to do is to reject enough knowledge and almost
anything becomes 'possible'."

We are speaking within the framework of classical physics, and its laws and
principles. Squareiods would not be possible unless there were some sources
of forces that would actually cause the planets to move in such orbits. 
Bombsies illustrate the very sort of failing that I see in classical
mechanics, its failure to say anything about consciousness.
Flying pigs are also very difficult to achieve, given the laws of classical
physics.

HPS:
>You admit that the gap in question is present. So you should admit
>that Zombies are possible within the logical framework provided
>by the classical laws and concepts. Raising the issue of other
>possible gaps obfuscates this main point.

PH:
"NO, it is absolutely central. I dont, in fact, think that zombies are
possible, but I dont think that the REASON they are impossible has anything
to do with the difference between one kind of physics and another."


I also think zombies are impossible; but the reason must have something 
to do with the nature of reality. If you believe they are impossible
then you should reject, as I do, a complete physical theory that 
allows them.


PH:
"It is full of such gaps (if I understand what you are here talking about).
Heres an example: the earth's magnetic pole keeps wandering around and
there is evidence that it reverses one in a while. Why? Last time I
checked, nobody had any idea. So theres an explanatory gap. WHY is this
'gap' different in kind than the 'gap' you refer to?"

The gap I refer to pertains to something that does exist but is 
not ENTAILED by the complete classical physical description of nature. 
But this description certainly does entail the existence, when they 
existed, of all of the earth-wobbles that have ever existed, 
that do now exist, or that ever will exist.

HPS:
>No further theory of the brain is needed to establish
>this elemental fact that, according to the classical physics
>conceptualization, (the description of) each brain is included in
>the classical physics theoretical desription of the the universe.
>This fact has been true for three hundred years, long before
>this century's great advances in understanding the brain.

PH:
Rubbish!  Did physics include a theory of brains before biology did? (If
this is true, then all Nobel prizes given to biologists should be
immediately rescinded.) How can something be 'included in the classical
physics theoretical desription' before it even exists?

I did not say "theory of brains", I said description of brains.

HPS:
>The essential REASON for the difference is that this latter
>gap is specifically linked to consciousness. It arises from the
>character of classical physical theory. That theory ties together
>everything that is built out of particles and fields into one
>highly coherent unified structure. But these laws and principles of
>classical physics do not bring consciouness into this tight structure

PH:
"They do not at present, but they might as we learn more. On what grounds do
you insist that this can never happen?"

PH:
"Look, isnt it obvious to you that you are here begging the question? How do
you know they enter so differently into the web of knowledge? Suppose that
by the end of the next millenium we come to understand how mentality is
physically realised. Then it WILL be completely entailed. Or, it may be
impossible to do this. But right now, we can't argue one way or the other.
You havnt pointed to any PRINCIPLED DIFFERENCE between 'experiental
content' and any other aspect of reality, other than a firm conviction you
seem to have that such a difference must exist (on what I am increasingly
coming to think must essentially be religious grounds, since your belief is
so unshakeable and so unjustified.)

"You insist that physics might completely account for the neural goings-on
in our heads, without ever mentioning the experiences we have. But maybe it
can't, in fact: maybe our expereinces ARE aspects of the neural activity in
our brains. I know you find this unpalateable, but what grounds do you
offer for your faith in the permanence of the 'explanatory gap'?"

I do not find this at all unpalateable: it is exactly what I believe
to be the case. I am seeking a way to make this compatible with
our fundamental  science, and eliminate the `explanatory gap'.

I the issue here is whether these advances can be achieved rationally within
the very rigid framework provided by the classical-physics conception
of the nature of matter.
 
You said: "Suppose that by the end of the next millenium we come to 
understand how mentality is physically realised. Then it WILL be 
completely entailed."

`Entailed by the complete classical physical description plus the
laws and principles of classical physics?' I although minor changes
in certain interaction terms could be made, those laws and principles
are fixed: what they entail now they will entail also in a thousand years.
The failings I cite are feature of the basic structure of the theory.

I have repeatedly pointed to a PRINCIPLED DIFFERENCE between the 
physical properties, as they are represented within the complete
classical physical description of nature, and conscious 
experiences as they are represented there. All the physical properties
are immediately and directly conceptualizable as structures in spacetime
that can moreover be conceived to be NOTHING BUT a collection of 
tiny particles and local fields moving about and changing in spacetime.
But experiences, though they can be regarded as transformations of such 
things, or translations of them into some other language, are not conceivable
as NOTHING BUT a swarm of such separate individual entities and localized 
fields. There is no way that a collection of such independent entities can
rigorously ENTAIL, using only the principles of classical mechanics, the 
existence of a feeling of sarrowness, and the quality and tone of that 
feeling. For the principles of classical physics simply do not give us any
grip that would allow us to pass from the concepts that classical mechanics
deals with to such a qualitatively different sort of thing. 
SOME added principle would be needed to bring  consciousness into classical
physical theory. But since the theory is logically complete without this
added principle, that principle is not part of the basic physical theory: 
it would be an ad hoc appendage. Without it zombies would be possible.


PH:
"If you find it obvious that `physical biology' can account
for our overt behaviour then... [PROVE IT]"

HPS:
>Proof:
>What I claim is obvious is that if the principles of classical
>mechanics were valid then the complete physical description in terms of
>particles and fields that these principles claim exists would
>completely specify our overt behaviours. This result is rigorous and obvious
>and trivially true because the complete physical description in terms of
>particles and fields specifies, according to the assumed principles,
>exactly where every particle and bit of energy is at every instant of time
>from the beginning of time to the end of time, and the assumed
>principles also assert that all physical objects are made up
>exclusively of these particles and bits of energy. But the behaviour
>of any system that is built exclusively out of tiny localized parts is
>determined by the changing locations and motions of these parts.

PH:
"ONLY if one also has an account of how the macroscopic system IS indeed so
constructed, and this account must permeate the entire fabric of science,
so that everything can be ultimately, in principle, etc., reducible to a
description in particle-and-field language."

HPS: 
The complete classical physical description of nature IS just that:
it is the description of the motion of every particle, and the
value of every field at every point, in the entire 
universe from the beginnig of time until the end of time.
It is only by considering this complete description that one can apply
the most general theorems: leaving parts out disrupts the integrity and
closure of classical physics.

Best regards, 

Henry