. Ma.rtin

Dr. Susan Haack

·~--·-----------

l'fUMBER

of Bristol

Bristol

CARi\TAP'S 'AUFBAU': SOME REFLECTIONS

By Susan Haack

The main acknowledged inspiration of Camap's Der logische Aufbau der Welt derives from Frege and Russell. Accordiilg to Carnap the logicists had teduced mathematics to logic: they had defined mathematical concepts in logical terms, and derived the Peano from logical axioms. Carnap followed Russell in hoping that it might be possible to do something analo­gous for empirical science, to reduce it to phenomenal terms. Russell had proposed that physical objects could be reduced to logical constructions out of sense-data. Carnap takes as the motto of the Aufbau Russell's com-ment in 'The relation of sense-data to , that:

The supreme maxim in scientific philosophlzing is thls: Wherever pos­sible, logical constructions are to be substituted for inferred entities.

And in the Aufbau he tries to do in deta:il what Russell had only sketched. Although, in his autobiographical sketch in Schillp (1963) Carnap records

that he studied Kant, and mentions a number of ways in which he was· influ-enced by this study, one fmds in the a very few, and rather casual, references to Kant. (The index of the lists just four references, of which only one, that to §162, where records his agreement with Kant's rejection of psychophysical dualism, is of any substance.)The object of the present paper is to draw attention to the fact that, although it is not clear that Carnap was fully aware of them, there are a number of very striking similarities, both in very general orientation and in very specific detail, between the Au.fbau and Kant's Critique of Pure Reason. Since my aim is rather to throw light on the Aufbau than to contribute to Kantian scholarshlp K shall not laboriously defend my interpretation of Kant; it will suffice for my purposes that my interpretation is a possible, if not the only possible, one.

Carnap offers what he calls a 'rational reconstruction' of empirical know­ledge. What he means by calling his system a 'rational', by contrast with an 'historical', reconstruction is, apparently, that he aims to represent logical relations, relations of definability, rather than temporal relations, relations of order of acquisition, between phenomenal and physical concepts. He imposes upon himself, however, the restriction that whatever kinds of object are chosen as basis must be 'epistemi.caUy prior', where epistemic priority is defined thus:

a is epistematically prior to b = df b is recognized via recognition of a.

This restriction is crucial to Carnap's choice of basis; for he believes that phenomenal concepts could. be defmed in terms of physical concepts, so that the order of construction, the choice of basis, is entirely underdeterrnined by

170

CARNAP'S 'AUFBAU': KANTIAN REFLECTIONS 171

the requirement of constructability. However, the constraint of epistemic priority, he thinks, requires the choice of a phenomenal basis. But the notion of epistemic priority seems to be essentially a temporal and a psychological, and in no sense a logical, one. Indeed, the inherently psychological character of the concept of epistemic priority becomes quite apparent when Camap argues that temporal cross-sections of the stream of experience, particulars consisting of one's experience at a moment, are epistemically prior to phe­nomenal universals, such as colours, smells, etc.; for Camap justifies this claim to the work of the Gestalt psychologists, thus revealing that he regards the daim as psychological.

Ostemibly, then, Carnap's programme is logical rather than psychological; but the Jntroduction of the constraint of epistemic priority brings in an in­escapably psychological element. It would scarcely be an exaggeration, in fact, to say that this ambiguity between a logical and a psychological system, or equivalently, a rational and a historical reconstruction, of empirical know­ledge, runs through the entire book. And here, already, one sees a similarity to Kant's Critique of Pure Reason. For although the Critique professes to offer an account of the necessary conditions of knowledge, what it frequently seems to be providing is, rather, something much more like an empirical account of the acquisition of knowledge. Logic and psychology, supposed ostensibly to be quite separate, are in practice almost inextricably intertwined. Kt would be an interesting, though a difficult, task, to investigate Kant's and Carnap's views of the proper relation of epistemological or logical and psycho­logical issues; for instance, Carnap, whose approach to logic is characterized by an emphasis on the question of the choice of formal languages, seems to distinguish logic from psychology more sharply than Kant manages to do.

The Aujbau resembles the Critique not just in the very general way already discussed, but also in some important details. The similarities between Carnap's construction and Kant's Transcendental Deduction (A), particularly, are remarkable.

Carnap chooses as the basic elements of his construction 'elementary experiences' (henceforth 'elexes'); that is to say, cross-sections of his sensory experience at a time, of some, unspecified, temporal extension. According to Kant one (though not the only) essential element of knowledge is intuition. 'Intuition' is used ambiguously between the event of intuiting and that which is intuited, but despite this ambiguity intuition clearly relates to a sensory input, with, apparently, some unspecified temporal extension. Elexes, hke intuitions, are sensory, temporarily extended, particulars.

Elexes are Carnap's primitive elements; as his single, primitive relation he chooses 'recollection of similarity', (Rs) which holds between two elexes a and b just in case a is earlier than, and resembles, b. Each elex occupies a certain temporal interval, and so Carnap is able to define temporal order,

172 SUSAN HAACK

exploiting th<:: fact that Rs holds between pairs of elexes the first of 1vhich is earlier than the a:; order of elexes. Kant stresses the impor­tance of the fact that intuition~ are, since belong to inner sense, in ·lc,~nn .. n11"·~i order_

Because elexes are the basic elements of lllis construction, they can't, Carnap somehow, to define, in terms of his

sensory sensory colours, smells, etc. And he proposes to do thls by means of whz'i' he calls a 'quasi analysis' of elexes into their

constituents'. he defines 'similarity circles', which are sets of elexes with one of a smaH number of similar properties in common; anol can then be defined in terms

circles. 1 shan't venture to comment on the success analysis into constituents as a

means of aren't really supposed to be analysable. My purpose is, rathe;·, to draw attention to the resemblance of Carnap's ambivalence on this to Kant's claims that each intuition is a 'unity', and yet 'contains a manifokl'.

In Carnap's construction, the temporal element in Rs is exploited to provide a means of defming the temporal order of elexes, and then the simi­larity element (two elexes a!e similar' -Ps-if either stands in Rs to the other) is exploited to provide a means of defining similarity circles and their quality classes. And these procedures, too, arguably have their analogues in Kant's account of the synthesis of the manifold. The 'synthesis of apprehen­sion', according to Kant, 'runs through and holds together' the manifold of intuition, while the 'synthesis of reproduction in imagination' unites like appearances. lit seems not to interpret thls account along the following lines; the synthesis of apprehension holds together a temporal sequence of intuitions, while the synthesis of reproduction in imagination then unites those intuitions which include a corrunon property; and these two processes begin to look much Wee the temporal and the similarity elements in Camap'sRs.

This is not, however, the possible interpretation of the role of the synthesis of rival interpretation would understand it as hold-ing together all the sensory at one time, rather than assembling a number of intuitions in order. If this interpretation were preferred there would be a contrast betv;reen Kant's construction and Carnap's; for Carnap stresses that Gestalt psychology has shown that, rather than getting discrete sensory inputs (sounds, smells, sights) and having to unite them, the sensory input comes as a whole. (But thls wholism is relinquished to some extent, of course, when he proceeds to engage in analysis, even if 'quasi analy­sis' of elexes.) Even on this second interpretation, however, although a con­trast emerges between wholist and Kant's more atomist approach,

CAR NAP'S 'AIJFBAIJ': KANTIAN REFLECTIONS 173

a similarity, between the definition of

My comments

of reproduction in imagination and the

the lowest levels of Carnap's universals are constructed

aim of the construction, of course, was sociological objects. Before

first constructs what he calls 'per-objects' wrrich an: in tum defined liia etc., objects. A

visual object, for , a stable visible persisting several elexes (e.g. the visual which features in all my elexes as

R ;..vriti:e a stable tactual the pencil felt); constructed out of the coincidence of

a are then constructed out by 1neans of what calls the

correspondence, as he puts between places and assignment of qualities to

K suggest that construction and the transcendental

can be seen between this part of Carnap's played in Kant's philosophy by the

'Transcendental object' is, notoriously, used ambigu-·traces o.f three senses are to be found:

l) transcendental are said to be constructed by us from intui-tions means of concepts.

but

2) transcendental are also apparently thought of, not simply in their role in synthes1s of as in l) but also by providing

an object m space, corresponding to that synthesis.

'While sometimes

3) transcendental are identified with noumena ('Noumenon' being of course, not

The first sense seems t.o be present in such passages as the follow-

All our are ... referred the understanding to some thus conceived, is only the tra;1scendental

object ... a correlate of t.he of apperception can serve only for the of m2nifold in sensibie intuition .... This transcen­dental object cannot be fron"l the sensible data .. .it is ... only the representation of appearances under the concept of an object ... (A250-l).

174 SUSAN HAACK

Transcendental objects in this sense, which are constructed by us from intui­tions by means of concepts, seem comparable to Carnap's perceptual objects, which are constructed from qualities themselves constructed from elexes appearing in stable A concept must be 'something universal which serves as a rule' (Al and in fact it looks as if the notions of concept and rule play much the same role for Kant as the notion of stable pattern, or regu­larity, plays for Carnap.

Transcendental in the second sense are more nearly analogous to Carnap's objects, which are iii physical, not visual, space. It would be a mistake to think of physical objects as analogous rather to nou-mena, or transcendenta!l in the third sense; for Kant, the, or rather, a, role of noumena would be to cause the intuitions which we unite ii1to trans­cendental objects in the first sense, whereas Carnap takes laws to hold between physical objects, not between physical objects and perceptual objects.

So far I have spoken of elexes, in as neutral a manner as possible, as 'cross­sections of the stream of experience'. But Carnap makes it clear that elexes are autopsychological objects, cross-sections, that is, of one's own stream of experience. C<unap describes himself as 'methodological solipsist', by which he means that his construction is a construction out of his own experiences. He doesn't deny that there are other people; it is just that other people are logical constructions out of his elexes. One's own body is defined as a visual object satisfying certain conditions, e.g. that each state of it is very close to the corresponding point of viev1, that every total state of it forms an open surface, that the qualities of tactile etc. sense classes are associated in certain special ways with it, and so forth. Once physical objects have been constructed, organisms can be defined as those physical objects which undergo certain pro­cesses such as metabolism and procreation, and then the class of men can be picked out, and hence the bodies of other persons. The experiences of other persons-hetero-psychological objects-are constructed on the basis of those physical objects which are the bodies of other persons using the 'expression' relation, a relation behveen certain movements of bodies and the psycho­logical events 'expressed' them. So Carnap, since he allows for the exist­ence, and for the psychological states, of other people, is hardly a solipsist of the traditional kind; since other people and their experiences are con­structed from his own experiences, he is a solipsist of some, as he puts it, a 'methodological', kind. But the concept of 'my' as opposed to 'another's' sensory experience, he comments, only makes sense once other people have been constructed, before which it would be more strictly correct to speak of the experience, which then can be called one's own, in an 'owner-neutral' fashion.

Kant maintains that transcendental apperception, the 'unity of conscious-ness' to wh:ich intuitions is 'the a priori ground of all concepts' (Al 07).

CAiRNAP'S 'AI[J!FJBAIJ': KANTIAN REFLECTIONS 175

H would not, I be fanciful to hear, in Carnap's 'methodological solipsism', echoes of the doctnne of the transcendental unity of apperception, nor to see analogies between insistence that physical objects, includ-

the bodies of other persons, are but logical constructions from auto-psychological and Kal1t's transcendental idealism.

Camap's observations that the description of elexes as one's own becomes speaking, only after the construction, out of

of other an argument better known from .Strawson's 'Persons'. But Ca~11ap's argument is worth compari.ng, also, with Kant's argument that X can't think of myselif as enduring cwcv~·'"-" time unless I make a distinction between permanent representations ond representations of the and recognize something permanent and outside me (B27 5, read of B XI). Pwd a further comparison also suggests this Hme with. 1-\362, where Kant apparently argues that whereas I always think of as the same person, from the standpo:iJ.1t of another person, to whom X am an object of outer intuition, there will be no grounds to infer the 'objective permanence of myself; Camap points out that each person has his own constructional system, and that in another's system I am a construction from his elexes.

'Ihe initial one of the Aujbau, with its structural approach, and its heal"; dependence on the apparatus of modern logic and set theory, is of a quintessenUally work. 'Ihis impression is confirmed by Carnap's acknowledgement of his debts to Frege and Russell. What I hope to have shown is not that this is in any way mistal-;:en, but only that the Aujbau can also be regarded from the standpoint of another, older, tradition. I should add, that, in pointing out the similarities between the and the 1[ don't mean to have denied that there are also notable dissimilarities, of which the radical empiricism of the Aujbau would be one of the most l

1 Thanks are due to Christine Battersby for helpful comments and criticisms.

IBlBUOGRAPHY

Carnap, R. Der iogische A u(bau der Welt ( 1928), English translation by George, R. A., Routledge and Kegan Paul, 1967.

Kant,!. Kritik derreinen Verrnmf,t edition 1781, B edition 1787), English translation by Kemp-Smith, N., IviacMillan, 1933.

Russell, B. 'The relation of sense-data to physics' in Mysticism and Logic, Allen and Unwin, 1917.

Schillp, P. A. (eel.) The Philosophy of Rudolph Cm·nap, Open Court, 1963. Strawson, P. F. Individuals, N!ethuen, 19 59.

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