The Problem of Other Minds, A Debate Between Scrodinger and Carnap

8/19/2019 The Problem of Other Minds, A Debate Between Scrodinger and Carnap

1/8

1

The Problem of Other Minds:

A Debate between Schrödinger and Carnap

Michel Bitbol1

CREA, CNRS/Ecole Polytechnique, 1, rue Descartes, 75005, Paris, France

Published in: Phenomenology and the Cognitive Science, 3 (1), 115-123, 2004

" All the premises on which science depends, when they are not of a purely

conventional nature, rest on experience". It is with this programmatic sentence that Carnap

concludes an article published in French, in 1936, in the journal Scientia. This article was

entitled "Existe-t-il des prémisses de la science qui soient incontrôlables?"2 (Are there

premises of science which are beyond control?).

If Carnap believed himself obliged, in 1936, to reaffirm a strict partitioning of analytic

and synthetic propositions, and if he regarded himself as having a duty to indicate again the

impossibility of a synthetic proposition being beyond empirical test, thus blocking any return

to some form of synthetic a priori, he took the opportunity first of all by responding to an

article of Schrödinger's which appeared a year earlier in the same journal, and was originally

written in French. The response to Schrödinger is nevertheless undoubtedly aimed, by way of

Schrödinger himself, at other philosophers such as Neurath, Schlick or Popper, whom Carnap

does not name but with whom a debate is underway in the mid-1930s3.

Schrödinger's article, modestly titled "Quelques remarques au sujet des bases de laconnaissance scientifique"4 (Some remarks on the bases of scientific knowledge), contains a

thesis which is outrageous for Carnap, explaining his prompt and vigorous response. That

thesis, all the more provocative to Carnap because it had been formulated by one of the

greatest physicists of the time, is as follows: "Science is not self-sufficient; it needs a

fundamental axiom, a basic axiom from without". An "axiom" which is radically outside the

system of science because it is neither empirically testable nor assimilable to a convention. A

basic axiom which Carnap thereby identifies as a trans-empirical premise which should be

called metaphysical.

But what is, then, this "fundamental axiom"? Schrödinger avoids stating the content of

it straight away, as if he sensed that even giving expression to it was going too far, and as if

1 Translated into English by Paul Tappenden. A preliminary version of this paper was first published (In French) in:Philosophia Scientiae, 3 (cahier 2), 203-213, 1999 (with the title: "L'alter-ego et les sciences de la nature, Autour d'un débat

entre Schrödinger et Carnap"), and also as chapter 2-13 of: Michel Bitbol, Physique et philosophie de l'esprit, Flammarion,

2000. 2 R. Carnap, "Existe-t-il des prémisses de la science qui soient incontrôlables?" Scienta LX, 129-135, 1936. 3 This point was suggested to me by Antonia Soulez. I should like, here, to warmly thank her for her careful reading of anearlier draft and for her constructive criticisms.

4 E. Schrödinger, "Quelques remarques au sujet des bases de la connaissance scientifique", Scientia, LVII, 181-191, 1935.On the Schrödinger-Carnap debate, see F. Nef, "A propos d'une controverse entre Carnap et Schrödinger", in M. Bitbol & O.

Darrigol (eds.), Erwin Schrödinger, Philosophy and the birth of quantum mechanics, Editions Frontières, 1992.


2/8

2

he anticipated an argumentative strategy of Carnap's wherein the most force rested, in the

end, on what was naïve in the explicit formulation of such an "axiom".

The beginning of Schrödinger's article consequently seems to be a long preamble

whose sole clear objective is to play for time. Then, after having underlined the impossibility

of a researcher himself rethinking every theory and, above all, of himself alone repeating all

the experiments which have led to the present state of his science, he starts to let his

fundamental hypothesis or axiom be glimpsed. He writes: "The sensory perceptions of

another human being are something which I have never experienced myself. Nevertheless, I

do not hesitate to interpret them by calling up the memory of what I call my own similar

perceptions". To be able to use a colleague's account of an experiment as if I myself had

made and recorded all the observations, continues Schrödinger, I must accord him "sensory

perceptions" like my own. The work of a scientist rests in the end on an anti-solipsistic

hypothesis which Schrödinger calls "Hypothesis P" (for the "Personality" of other humanbeings) but of which Carnap alone, it must be emphasised, gives a synthetic version of in his

reply to Schrödinger:

" Hypothesis P: It is no only I who have sensations (and consequently thoughts,

feelings, memories, etc.); other human beings have them too".

That this hypothesis cannot be "verified by exact scientific method" (or rather that it is

beyond "empirical control", as Carnap preferred to say following his then recent critique of

verificationism in Testability and Meaning) is certainly not a circumstance which is

accidental or auxiliary so far as Schrödinger is concerned. It is not just that all the

observations which I am capable of making of the behaviour of another person are equally

interpretable either in terms of neurophysiological processes or in terms of sensations and

thoughts, but that the second type of interpretation (which would tend to confirm Hypothesis

P) must necessarily, methodologically, be rejected in a particular framework of scientific

explanation. To demonstrate this, Schrödinger chooses a very simple illustration: I pinch

another man; the man will perhaps make an exclamation, but wouldn't that be the way in

which an automaton reacts to being pinched? On one hand, says Schrödinger, we indignantly

reject this degrading suggestion according to which the alter-ego could not be anything but an

automaton, but on the other hand we must insist that the physiologist gives a systematic

treatment. If we ask why the man makes an exclamation, Schrödinger continues, would you

believe that a physiologist (in the rôle of physiologist) would be inclined to reply that the man

made an exclamation because he felt a pain? Certainly not, because in replying in that way

the physiologist would be ignoring the genuine scientific problem.

The physiologist who would insert into his account of neuronal processes a reference

to what is felt by the owner of the nervous system would thereby merely show his partial

ignorance of the class of phenomena he is responsible for elucidating. Even more seriously, if

he regularised the surreptitious involvement of Hypothesis P in his explanations, he would be


3/8

3

in great danger of falling back into some sort of vitalism, or of returning to the invocation of

entelechies.

The physiologist is in fact bound to conform to a way of thinking which no-one has

ever accepted overtly, but which characterises the scientific enterprise from start to finish.

That way of thinking, which Schrödinger puts into a dramatic setting at the end of his Nature

and the Greeks (1948)5, and then in his 1956 book Mind and matter6, is that which moves

towards objectivising. In striving to construct our representation of the external world, he

writes, we have used a simplifying device which involves the exclusion of ourselves: "The

scientist subconsciously, almost inadvertently, simplifies the problem of understanding

Nature by disregarding or cutting out of the picture to be constructed, himself, his own

personality, the subject of cognizance"7. That is exactly the reason why the scientific picture

of the world does not itself contain any ethical values; nothing about esthetics, no word of our

ultimate aims and destiny8

. Nevertheless, this melancholic observation does not amount to aninvitation to regress. Once his work is determined by opting for objectivising, that is to say,

by opting to subtract from our representation of the world everything which is proper to "the

subject of cognizance", the scientist must follow through. He must never again head back

towards a lost paradise which Schrödinger refers to, following his reading of The Advaita

Vedanta and then Schopenhauer, as the domain of a mystic unity between minds and

between the One-Mind and the world. Objectivising, for Schrödinger, thus involves neither

the contingency of fact nor the indifference of convention; it has the imperative character of a

commandment to which Heraclitus gives voice in his fragment 2: "It is therefore necessary to

follow the common. But while reason is common, the majority live as though they had a

private insight of their own"9.

For Schrödinger, the seemingly paradoxical reason why Hypothesis P has no place in

scientific discourse is that the mode of scientific discourse is wholly supported by it; it is the

background of science (in a sense close to that intended by John Searle10); it will not be seen

amongst the resolutions put forward by science. The elements of Hypothesis P cannot count

amongst the properties of the ob-jects of scientific knowledge, not even when those objects

are human beings. Schrödinger points this out in a sentence of his 1935 article. Hypothesis P

is not scientific, he insists, and that "(...) prohibits mentioning it in the very dealing with a

scientific problem, in spite of , and perhaps because of the fact that science in its totality

5 E.Schrödinger, Nature and the Greeks, Cambridge University Press, 1948, and (in French translation), La nature et les

Grecs, prefaced by La clôture de la représentation , M.Bitbol, Seuil, 1992. 6 E.Schrödinger, Mind and Matter (with What is life?), Cambridge University Press, 1967, and (in French translation), L'esprit et la matière, prefaced by L'élision , M.Bitbol, Seuil, 1990. 7 ibid., p.90. 8 E.Schrödinger, Nature and the Greeks, op. cit., p.95. 9 ibid. p. 70

10 J. Searle, Intentionality, Cambridge University Press, 1983, p. 143... insert original English quote beginning "Thebackground is 'pre-intentional' in the sense that though not a form or forms of intentionality, it is nonetheless a precondition

or a set of preconditions of intentionality". It amounts to a knowing-how rather than a knowing-that.


4/8

4

depends on that hypothesis". This exterior character of the foundation of the sciences would

undoubtedly seem unacceptable to a philosopher for whom the scientific method constitutes

the exclusive test of the validity of propositions, and for whom, consequently, no proposition

must in principle be placed beyond the reach of that method, even, and perhaps above all,

where its own premises are concerned. But Schrödinger, who holds for a long time that

"physics does not reduce to atomic physics, nor science to physics, nor life to science" 11, is

not affected by that exterior character at all. On the contrary, according to him the scientific

ex-territoriality of Hypothesis P enables it, to its credit, to provide one of those signs, at once

ambiguous and undeniable, of the rootedness of the sciences in a lebenswelt which always-

already came before it12. As Schrödinger writes in his 1935 article, he does not even think

that science needs to regret the fact that one of its principal pillars rests on non-scientific

ground; for it is thus that science links itself more directly with other human thoughts and

aims than if it existed in and of itself.In making his reply, Carnap does not radically doubt Schrödinger's Hypothesis P. He

shares ("obviously", he would say) the anti-solipsism of his interlocutor. But his way of

defending this position in 1936 shows signs of an evolution in his thinking which had taken

place since the appearance in 1928 of Der logische Aufbau der Welt 13.

In the Aufbau, Carnap chose to adopt a position which he qualified as "methodological

solipsism"; that is to say, to proceed to the construction of the world from "auto-

psychological" material. Methodological solipsism was clearly distinguished throughout the

work from some sort of metaphysical solipsism. One of the most acute remarks which serves

to establish this distinction is that the characterisation of the basic elements of the

constructive system as "auto-psychological" and as "mine" does acquire a meaning only after

the domain of the non-psychological (and, to begin with, of the physical), as well as of the

"you", have been constructed14. To put it another way, the characterisation of elements as

"mine" has no meaning other than in opposition to the things which are "theirs" and "yours"

and which constitute at once one of the products of the construction and its point of departure.

In his 1936 text, on the other hand, Carnap bases his metaphysical anti-solipsism on

an argument which is borrowed from the article "Physicalismus" published by Neurath in

1931, and which arises from what the latter called "social behaviourism". According to

Carnap, it is legitimate to infer the possession of feelings, thoughts, memories and

perceptions by someone on the basis of a "determinate exterior behaviour". That inference is

just as legitimate as that which allows the derivation of the intensity of an electric current in a

11 E. Schrödinger, letter to W. Wien 25 August 1926, in K.Przibram (ed.), Letters in Wave Mechanics, PhilosophicalLibrary, 1967. 12 The use of the Husserlian (and Diltheyan) term 'Lebenswelt' serves to underline such an insistent reference by Schrödinger

to the rootedness of science in "life" that it sometimes has the tone of Husserl's Krisis. However, there was not, so far as I

know, any direct influence on Schrödinger from either Dilthey or Husserl. 13 R. Carnap, The Logical Structure of the World , Routledge and Kegan Paul, 1967. 14 ibid. p.201.


5/8

5

wire on the basis of quantities measured such as the rise in temperature of the wire or the

deviation of a magnetised needle placed in the vicinity of the wire. Just as the physicist would

never think of doubting the existence of the current in the wire because he could not himself

be the wire and establish from the inside that by which the current manifests itself

experimentally, so the psychologist must not doubt the existence of the feelings, thoughts and

sensations of others because he cannot merge with others and establish from the inside that

which motivates their behaviours. The proposition according to which other human beings

have feelings, thoughts and sensations is in the end experimentally testable on condition that

we allow only exact relational laws linking mental states with behaviours. Hypothesis P, in

this modest version which Carnap favoured and labelled P1, thus does not elude empirical

control. Only a strong and metaphysical version of Hypothesis P, labelled P2, which would

return to postulating the impossibility of establishing a law-like relation between mental

states and behaviours would remain beyond the reach of control by experience. But, Carnapadds, only the modest version P1 of Hypothesis P counts amongst the premises of scientific

work. And consequently, he believes himself warranted to conclude, the type of anti-

solipsistic premise demanded by science is empirically testable.

What are we to make of this debate and the arguments put forward by the two

protagonists? I find it quite striking that throughout their discussion both Schrödinger and

Carnap, without wishing to, occupy ground which gives too much purchase for the others'

arguments; and that they thereby weaken their ability to defend their real theses.

Let us see first of all how Schrödinger puts himself in a position which gives an

advantage to Carnap. As we have seen, Schrödinger shows at the beginning of his article a

certain reluctance to say just what is this extra-scientific background of the scientific

enterprise, the existence of which he invokes without spelling it out. But he ends by

presenting the elements of a description which Carnap can afterwards rearrange, and he goes

so far as to endow it with the status of an "hypothesis" or "axiom". Schrödinger, despite

himself, thus puts his "fundamental hypothesis" within the sphere of the propositions of

empirical science; a sphere where some propositions implicitly have the status of intangible

premises and where others are in the position of being experimentally tested, but where none

is intrinsically sheltered from empirical testing. Carnap is right under these circumstances to

emphasise that there is no reason why Hypothesis P should in principle be exempted from

empirical control. The expression of Hypothesis P, however much it is shielded from doubt,

like a "hinge" on which doubt turns15, cannot take advantage of any other justification but this

function of being a fixed point in the network of reasoning in order to escape de facto (and

not de jure) from a process of experimental testing. Even if we urge that Schrödinger has

good reasons to believe that that proposition, or at least what underlies it, is truly outside the

15 L. Wittgenstein, On Certainty, Basil Blackwell, Oxford 1969, §341.


6/8

6

ordinary domain, the fact of having included it amongst the propositions serving as explicit

premises of empirical sciences cannot but expose it to being subjected to ordinary treatment.

Reciprocally, Carnap makes enough concessions to Schrödinger to weaken his own

arguments. Carnap concedes, for example, that it is necessary to rest the scientific enterprise

on a belief in the perceptions and thoughts of other human beings. From then on, all his

efforts consist in demonstrating the validity of an inference from that which is experimentally

accessible to that which is not; from behaviours to perceptions and thoughts. Unfortunately,

the inductive character of this inference leads Carnap to loose sight of the under-

determination of his mentalistic explanation by the behaviours explained; that is to say, the

fact that even if the mentalistic account is sufficiently corroborated it is undoubtedly not the

only acceptable one. From then on he cannot see the subtlety in Schrödinger's line of

thinking. The latter did not, in effect, propose to separate the mentalistic account from the

domain of possible explanations of behaviour other than by comparison with a purely physiological type of explanation. Schrödinger did not deny the plausibility of the mentalistic

account; he even went so far as to admit that the physiological account is less satisfactory

because generally incomplete. But he did not hesitate, despite that, to exclude the mentalistic

account from the class of scientifically acceptable explanations and to himself prefer the

physiological account. And if he excluded mentalism, it is that he thought that the mentalistic

account of behaviours was profoundly at odds with the founding aim of science, namely the

objectivisation. We would say nowadays that Schrödinger had rested his affirmation of the

intangibility of Hypothesis P on the pragmatico-transcendental principle which consists in

making manifest the performative contradiction which arises in the practice of a science

conditioned by objectivisation whenever it attempts to make use of a type of explanation of

which, until better informed, all the elements cannot be considered as objectivised.

Let us now imagine that neither Carnap nor Schrödinger had made such advances

into each others' territory. Suppose that Schrödinger had not given Carnap to understand that

the background of science could be expressed in the form of a proposition labelled

'hypothesis' or 'axiom', and that Carnap, for his part, had not conceded to Schrödinger that

science requires amongst its premises the proposition according to which other human beings

have perceptions and thoughts similar to mine. Schrödinger and Carnap would then have been

able to agree on this: the point of support of science is not an explicit assertion concerning

what other human beings see and think; it is simply a practice of communication which

anticipates or presupposes the prefect interchangeability of positions amongst the members

of the linguistic community. The belief in thoughts analogous to my own for other human

beings, the mentalistic vocabulary of folk-psychology, used by Carnap, as by Schrödinger, do

not take first but last place in this perspective; because these devices do nothing but express

after the event the confidence to which the disputants bear witness regarding a generally

successful practice of communication. The difficulties only arise when we accord to this

retrospective verbal expression of mutual understanding the position of the process of mutual


7/8

7

understanding. But, we will ask, how can we do otherwise; how are we to express the

primeval understanding without giving it the form of propositions by which we come to

interpret it once its first step has already been taken?

Maybe in asking a poet, in this case Paul Eluard, to effect the desired mediation

without compromising us with a psychologising language which comes, inevitably, too late.

"Ce n'est pas plus difficile de parler avec les oiseaux qu'avec n'importe qui sur terre:

tu parles, l'oiseau fait celui qui a compris, il te répond et tu fais celle qui a compris; et tu

réponds à ton tour" (It is no more difficult to speak with the birds than with anyone on Earth:

you speak, the bird acts the one who has understood, it replies to you and you act the one who

has understood; and you reply in turn)16.

It is not here a question of comprehension, of perceptions or of thoughts, but of acting

the one who has understood, who sees or who thinks. No inference from behaviour to

"interior" representations, but nothing either to favour a reductionist behaviourism whichwould not see anything but isolated gesticulations there, instead of the play of echoes and

reciprocities by which an understanding manifests itself. Picking up on a remark of J.

Bouveresse's concerning the Wittgensteinian concept of a rule17, we should say this: it is only

for someone who takes communication as a form of recognition which is purely external,

reduced to behaviour as a simple anthropological fact (human beings emitting sounds and

making movements) that the ideas of significance and expression disappear. From the point

of view of internal recognition, that is to say, for someone who effectively participates in

verbal and gestural exchange, utterances signify and gestures express, without its being at any

time indispensable to support the signification and expression on the explicit belief in their

mental counterparts. In place of the difference between mentalistic and neurophysiological

accounts of communication there is substituted a much more decisive difference between the

engaged conduct of the speaker and a multitude of disengaged accounts variously produced

by the ethnologist (behaviours), or the physiologist (neuronal processes) or even the

psychologist (mental processes).

If they had recognised that, Schrödinger and Carnap would have had no difficulty in

being in agreement. Schrödinger would have admitted that as soon as the dynamic of

understanding translated into the form of a proposition, it finds itself projected onto the same

plane of disengagement as that of the propositions of natural science, none of which is

intrinsically beyond empirical control. He would have also recognised that the use of the

terms 'hypothesis' or 'axiom', including when qualified as "fundamental" and when expressed

with the help of a psychologising vocabulary which would make claim to being closest to the

point of view of the speaker, really does nothing but manifest the partially disengaged

position of he who speaks of it. What other word than 'hypothesis' must we use under these

16 P. Eluard, Grain d'aile, Rouge et Or. 17 J. Bouveresse, Le mythe de l'intériorité, Minuit, 1987, p.56.


8/8

8

conditions? Surely not 'convention', which encompasses a dimension of intersubjective

agreement, and which thus presupposes that which it is meant to express. Perhaps, then, it

would be more suitable to invoke some " form of life", or better still, as Wittgenstein

proposed in On Certainty, a Weltbild which might be thought of as the integrated and active

totality of forms of life:

"I say Weltbild and not hypothesis, because it is the matter-of-course foundation for

his research and as such also goes unmentioned"18

Once this move is made, Carnap could have for his part understood without difficulty

Schrödinger's insistence on placing his Hypothesis P beyond the reach of the empirical

control applied to propositions of a factual form; because what Hypothesis P tries, a little

clumsily, to translate is not really an hypothesis, nor an axiom, nor a proposition, but rather

the pre-condition of a linguistic practice which puts into play hypotheses, axioms and every

other sort of proposition.One can sometimes get the impression, on reading the articles of Schrödinger and

Carnap, that these two authors came within an inch of the pragmatic turn of which I have

been making myself an advocate. Consider Schrödinger: when he says of his hypothesis not

that it is simply evident or commonly accepted, but that it is "very, very, very evident"; or

when he admits that if he is absolutely sure that one hypothesis is correct then he has only to

build on it without concerning himself with the reasons for his certitude. He then recognises

that the explicit acceptance of his Hypothesis P is indispensable neither in the course of

communication nor in the practice of science. As for Carnap, he goes even further in this

direction in writing in his response to Schrödinger that, without doubt, in everyday life the

relational laws between behaviours and mental events are not explicitly formulated but tacitly

presupposed and applied.

Carnap and Schrödinger did not, however, draw all the consequences from their

remarks. It is easy to understand why. Carnap was committed to the Weltbild of logical

positivism, which drove him to ignore the transcendental dimension of the pragmatic and to

not attribute to it anything more than the status of empirical knowledge19. Schrödinger, for his

part, was a late representative of the Weltbild of German post-Kantian idealism, which

included amongst its tasks the metaphysical hypostatisation of performative backgrounds.

The core, at once minimal, global and universally shared, of the Weltbild which pre-

conditions simple communication could not be sufficient in itself to reduce the divergence

which was in place between the two historic Weltbilder in which Carnap and Schrödinger

enlisted themselves.

18 L. Wittgenstein, On Certainty, op. cit., §167. 19 The definition of the pragmatic which Carnap gives in Meaning and Necessity (University of Chicago Press, 1958, p.233)is exactly in this vein: "... pragmatics, that is, the empirical investigation of historically given natural languages".

Documents

The Problem of Other Minds, A Debate Between Scrodinger and Carnap