realism and the aim of science.by karl popper; w. w. bartley;the open universe: an argument for...

Mind Association

Realism and the Aim of Science. by Karl Popper; W. W. Bartley; The Open Universe: AnArgument for Indeterminism. by Karl Popper; W. W. Bartley; Quantum Theory and theSchism in Physics. by Karl Popper; W. W. BartleyReview by: Anthony O'HearMind, New Series, Vol. 94, No. 375 (Jul., 1985), pp. 453-471Published by: Oxford University Press on behalf of the Mind AssociationStable URL: http://www.jstor.org/stable/2254816 .

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Critical Notices 453

with one's 'present self'. This seems to me the theory a proponent of the Self-Interest Theory should move to if he becomes persuaded of Reductionism and of the claim that what matters is psychological C&C, and if he wants to retain the spirit of his original view. And this theory poses as great a threat to the

rationality of morality as does the original Self-Interest Theory.5 Parfit does mention such a revised version of the Self-Interest Theory, but what he says about it does not seem to meet the point just made. One thing he says is that the revision 'breaks the link between the Self-Interest Theory and what is in one's own interest' (p. 317). But this is true only on the old conception of what is in one's interest; and, in any case, he says nothing to show that it breaks this link in a way that helps morality. He also says that the revised theory is not a version of the Self-Interest Theory and is instead a version of what he calls the 'Critical Present-Aim Theory'?a theory which says that what it is rational for one to do is whatever best achieves what, at the time, one (not irrationally) wants or is

rationally required to want. But elsewhere he tells us that any theory, even

including the original Self-Interest Theory, can be construed as a version of the Critical Present-Aim Theory?so the fact that the revised theory is a version of it is no reason for saying that it is not also a version of the Self-Interest Theory. I am not of course recommending the revised theory; my point is only that if the

original Self-Interest Theory needs to be refuted if we are to defend the rationality of morality then so does this one, and that it is not refuted by considerations about what matters in personal identity. (It may be that a sufficient argument against both theories is that they do imply the irrationality of desires to help others or do one's duty; this seems to be what Parfit's first argument against the Self-Interest Theory in Part Two amounts to.)

Parfit's discussion of personal identity is full of rich and fascinating detail? much more than I have been able to cover here. Like all of the book, it amply repays careful study. It is a compliment to the book, as well as a complaint, that in reading it one acutely feels the lack of a subject index. It is much to be hoped that future readers of the book will have the benefit of one. It is to be hoped even more that the book will have the many future readers it deserves.6

Cornell University sydney shoemaker

5 Here I am indebted to Richard Moran. 6 I am grateful to D. Brink, R. Farr, H. Hodes, P. Gasper, A. Sidelle, J. D. Trout, M. Wachsburg,

and J. Whiting for helpful comments on an earlier draft of this review.

Realism and the Aim of Science. By Karl Popper. Edited by W. W. Bartley III. London: Hutchinson, 1983. Pp. xxxix + 420. ?20.00.

The Open Universe: An Argument for Indeterminism. By Karl

Popper. Edited by W. W. Bartley III. London: Hutchinson, 1982. Pp. xxii + 185. ?15.00.



454 Anthony O'Hear

Quantum Theory and the Sehism in Physics. By Karl Popper.

Edited by W. W. Bartley III. London: Hutchinson, 1982. Pp. xviii +

229. ?15.00.

These three volumes, referred to below as RAS, OU, and QTSP, respectively, comprise Popper's Postscript to his Logic of Scientific Discovery. The books have existed in some form in proof since 1956-7, but the present volumes include more recent introductions and notes.

What are the main concerns of Popper's three-volume Postscript? At first sight they seem a somewhat disparate collection: realism and the aim of science, the role of metaphysical conceptions in science, the problem of induction, the

propensity theory of probability, indeterminism, human freedom, quantum theory. All are part of a concerted attack on epistemological subjectivism, and, at the same time, part of a defence of human rationality and creativity. There can be no

doubting the seriousness of these themes and the earnestness of Popper's rhetoric.

How, though, do the themes interconnect? Realism for Popper means that scientific theories aim to tell us unsuspected

truths about the entities and processes which underlie the phenomena we have

experiential access to. We are not, then, stuck with what we can observe, whether we regard what we observe as sense data or middling-sized objects in experiential space or even what we can observe through scientific instruments. Thinking that our knowledge is to be confined to and analysed and justified in terms of observable data is, according to Popper, the fundamental root of subjectivist and justificationist epistemologies?epistemologies that would in various ways confine our knowledge to what we can experience, and to justify it in terms of our experience.

There are links here with both induction and quantum physics. With induction, because induction is really the attempt to justify beliefs about what we do not know on the basis of things we have experienced. All such attempts are, in

Popper's view, invalid. Not only that?and this is the link with subjectivism? they are also quite misguided in their implicit assumption that there can be any reduction of our theories or beliefs about the world to experience. These all go way beyond experiential proof, but are not the less acceptable for that. We should

give up the compulsion to prove and justify, which is itself a facet of the

subjectivistic idea that there can be no more to knowledge than is given in

experience. Quantum physics has proved a fertile ground for subjectivism, because some of its interpreters, notably Heisenberg and Bohr, have read its formulae as

implying that the data themselves are in some sense made real by observation, and do not really have definite states, independently of observation.

Popper believes that on the contrary they do, and that the illusion that they do not is fostered by a failure to realize that many of the theories of quantum physics are probabilistic. They say that a given particle, say, in a given position, will be in one of a number of possible states of momentum, and that it is not

possible on the theory to predict which. Of course this does not preclude its

actually being in one or other of those states, nor does it entail that when we discover which, we have somehow brought that about.

Quantum physics appears to be ineradicably probabilistic. The world it describes is indeterministic. Things and events there cannot be precisely predicted.




All we can say is that situations of certain types regularly turn out in certain

ways according to certain frequencies. Half of a given population of uranium atoms will regularly have decayed over a given number of years, though we cannot

say in advance which individual atoms will have decayed, nor when any individual will decay. Nevertheless, producing these statistical regularities are certain real

propensities or tendencies inherent in situations of a given type, in the same way that a real force?gravity?keeps the earth in orbit round the sun. A metaphysical realism about forces in determinist theories is paralleled by a metaphysical realism about propensities in statistical theories. In both cases regularities at an observable level are explained in terms of underlying forces at an unobservable level.

The human world is indeterministic, even apart from quantum theory. There would be something self-defeating about believing that our own states of knowledge were determined; it would undercut any claim that a belief, including the belief in determinism, was rationally held. So rationality and hence, presumably, objectivity in our knowledge depend on the truth of indeterminism. And the statistical theories that indeterminism leaves us with are not to be seen subjectively as confessions of ignorance, as would be implied on a deterministic view of the

world, where, if only we knew enough, we could, like Laplace's intelligence, foresee in precise detail every future state of every system. They are to be regarded as fully objective, underpinned by real propensities the world has to follow given patterns.

It cannot be said that any of this would be unfamiliar to careful readers of those works of Popper's which had been published before the Postscript. This is neither a criticism of the Postscript, which was, after all, substantially written by 1953, nor totally unsurprising. Bits ofthe Postscript have actually been published already, and many of the ideas of the unpublished parts have been published in

other writings by Popper and others. But the Postscript will be disappointing for

anyone hoping for any radically new or surprising developments in Popperian thought. Even the more recent footnotes and introductions add little to any debate

on-going since the 1960s. In what follows, I will concentrate mainly on the two areas of thought which

seem to me most central and, in a way, most questionable in the Postscript. These

are Popper's defence of realism and his development of a propensity theory of

probability. They are central to Popper's world-view, but have not, in my opinion, been discussed by Popper's critics as seriously as they deserve to be. In the

Postscript these topics are given the prominence they clearly have for Popper. Realism, Popper says (RAS, p. 81), forms a kind of background that gives

point to our search for truth. Rational discussion would be pointless without an

objective reality, a world which we make it our task to discover, unknown or

largely unknown. The role of our observations in this picture of science probing worlds beyond our knowledge is simply to test and check our theories about these

worlds. We must avoid the subjectivistic trap of wanting to see what we know

reduced to and justified in terms of our sense experiences. This is the route to

idealism and solipsism; against these doctrines Popper finds that 'realism is so

obviously true' that straightforward counter-arguments are trite and distasteful,

though I must say that I found Popper's argument against solipsistic idealism

charming. (It is that I know that there are minds other than my own, because I

am certain that I?Karl Popper?have not and do not have it in me to write



456 Anthony O'Hear

Bach's music or the Iliad or the Inferno or The Tempest, or indeed, advertising slogans and jingles.)

Let us grant Popper that Bach existed, that he, not I, was responsible for the

Goldberg Variations, and that in many other ways the world, natural and human, has properties that are unsuspected by me or indeed by anyone now living or

who has ever lived. There is a real world through which we and other conscious

beings make our inevitably partial and limited journeys. The world is not reducible to the experiences we have of these journeys, individually or collectively. This would be a perfectly familiar and respectable form of realism, in opposition to

equally familiar doctrines such as idealism, solipsism, or phenomenalism. But what is quite unclear is that a moderate realism about the observable world, such as the one just suggested, also commits one to a realism about unobservable or theoretical entities, such as forces or propensities or even electrons. What I mean is this. At the bottom of the ocean, there may be beings no one will ever see, and

quite different from anything anyone has ever imagined. But accepting the truth of this statement is of quite a different order from accepting that there are such

things as mesons and muons. Popper's realism embraces both strange fish and

mesons, to say nothing of unobservable forces and propensities, and appears to make no distinction between the one and the other; indeed, he appears to put both on the same footing as tables and chairs.

The reason for this is that, in Popper's view, 'all our knowledge is interpretation in the light of our expectations, our theories, and is therefore hypothetical in some

way or other' (RAS, p. 102). Thinking of an object as a glass of water is for

Popper to engage in theorizing and hypothesis, in essence no different from

reading something on a radar screen as the path of an oncoming aircraft. There is no uninterpreted datum on which to found certain knowledge; to think there is would be to entertain a subjectivist illusion. And here we can see a link in

Popper's thought between his brand of realism and his hostility to induction and

justificatory epistemology. The real world comes to us through conjecture and inborn dispositions to interpret data in particular ways. Our interpretations are, and must remain, conjectural, and the subjectivist hope of finding a secure basis for knowledge is forever doomed. 'If realism is right, the aim of the subjectivist theory of finding a secure subjective basis upon which to erect our knowledge of the world?and sound reasons for a belief in the reality of the world?is an unrealizable and, indeed, an unreasonable aim' (RAS, p. 102). But once we realize that our beliefs that this is a table or that surface is red are conjectural, we can

see, against instrumentalists such as Berkeley, that the difference between Newtonian dynamics, which asserts the existence of real but unobservable forces, and ordinary statements of ordinary language about red tables and so on is only a matter of degree. Each category is made up of unverifiable conjectures about a

real, but ultimately inaccessible world. Bas van Fraassen has written: 'We have to make room for the epistemological

position . . . that a rational person never assigns personal probability 1 to any proposition except a tautology. It would, I think, be rare for a scientific realist to take this stand in epistemology, but it is certainly possible.'1 The fact that van Fraassen could have written this without even referring to Popper in a footnote

1 The Scientific Image, Oxford, Clarendon Press, 1980, p. 9.




as being someone who does with great vigour and repetitiveness just what is said to be rare is, I think, indicative of the way Popper is often ignored in current debates about realism and truth in epistemology. (Rorty, for example, does not mention him at all.) But despite the fact that the Postscript was written more than

25 years ago, the blame for this sad state of affairs is at least partly Popper's. His construction of realism and the defence he mounts of it seem hardly to engage many of the issues prominent in current discussion, and this does matter because at least some of these issues do have a bearing on Popper's claims. Popper seems to regard the main threat to a thorough-going realistic attitude to seientific theory as deriving from the sort of instrumentalism which treats seientific theories as

nothing but instruments for prediction. Popper counters this type of in? strumentalism by pointing to 'profound differences' between theories and tech-

nological computation rules, such as the universality of theories, their falsifiability, and the possibility of mutual inconsistency between theories which make the same

predictions in their areas of present testability. Popper regards the possibility of future crucial experiments in this last case, and the way in which we regard theories as unsatisfactory and indeed as falsified if their applicability is less than

universal, as evidence of the fact that scientists do regard their theories as

describing the structure of reality, even where direct observation of the entities

postulated in the theories is not possible. He goes on to say that instrumentalism is anti-rationalist, implying 'that human reason cannot discover any secret of our world' (RAS, p. 123) and that science is mere technique. (His animus against the

Copenhagen interpretation of quantum theory is largely due to its implication that so long as a theory delivers the goods we need not worry about apparent inconsistencies or conundra in the interpretation of its formulae.)

Popper's philosophy of science is, to use a phrase of Ian Hacking's, ineluctably 'theory-led'. That is to say, he sees the aim of science as being to explain particular phenomena by seeing them as deducible from theories expressed in universal form. If a universal theory makes predictions of further phenomena independent of those originally to be explained, and these predictions survive testing, then the

theory may be regarded as having a positive degree of corroboration. Corroboration increases with the improbability of the theory and the severity of the tests it survives. What we are being given, in effect, is a claim that the theoretical

explanation of observable data gives a reason of some sort for belief in the unobservable entities and processes postulated by the theory in question. It is

just this claim that has come to seem increasingly questionable, and which the

Popperian arguments against instrumentalism do not seem to touch. The basic reason for this is that any set of predictable or observable effects can be deduced from a great number of theories, mutually inconsistent in terms of internal structure and unobservable entities. The fact that one explanation of a given set of effects rather than some other is proposed would seem to depend on historical accident: the unobservable entities and processes thus proposed would, it seems, be accorded their existence by grace of history rather than by anything intrinsic to physical reality. This point can be admitted even if we do not go so far as to say that where two or more logically distinct theories are equivalent in respect of observational consequences there just is no fact of the matter which would make one true and the other false.

Popper speaks of it being a 'highly improbable coincidence' if a theory like



458 Anthony O'Hear

Einstein's predicted correctly very precise measurements not predicted by its

predecessors unless there were some truth in it.2 He goes on to connect this point with the 'vague realist assumption' that reality is in some respects similar to what science tells us. What sort of an argument is this, as an argument in favour of seientific realism? Couldn't a Newtonian quite legitimately have deployed such an argument to prove the existence of absolute space and time, and even of the

world as the sensorium of God? Of course we know, and Popper knows this better than anyone, that Einstein's theories are likely to be refuted, as Newton's were. What seems to follow from the history of refutation in science is that the world is really quite unlike what even the best seientific explanations of any given time would have us believe. So the counter-argument to realism in respect of the unobservable elements of successful explanations is not just theoretical. It would seem to be urged on us by the replacement historically of one model of explanation by another. Popper is, nevertheless, quite right in finding some truth in Einstein, and more truth there than in Newton, but there is no need to envisage and rule out highly improbable coincidences to account for this. The 'some truth' in Einstein just is its accurate predictions of very precise measurements (more precise and more accurate than those of its predecessors).

It will be objected here by orthodox Popperians that Popper, at least officially, does not argue we have any reasons for believing in the truth of any theory, however successful and well-corroborated. On the contrary, he generally dismisses

any such suggestion as inductivist and justificationist. He speaks of acceptance and acceptability of theories in distinction from belief in their truth, and simply in terms of their testability for the future. We accept an unrefuted theory until such time as we succeed in refuting in it, and in the expectation that we will refute it. Because of this, I am unclear that Popper would actually need or want to say that there was any surplus of truth in Einstein's theory over Newton's than in its better-corroborated predictions. In fact, despite the 'improbable coincidence' argument, he generally warns against drawing any conclusions from the success of our theories, saying that (in view of the fact that all our theories are almost certainly false) any such conclusions would prove too much. Thus we should not say that Einstein's theory is probably true because it is successful, because we will even more probably eventually find it is unsuccessful because it is false. In fact, Popper's growth of knowledge really comes down to a growth of

knowledge that more and more specific theories are false, together with a growth of knowledge about particular, mosdy observable data?new planets, more accurate measurements of data, and in some cases, to be sure, new types of data from new

types of observation. The anti-realist criticisms I am making against Popper do not require that we draw in advance a sharp line between the observable and the unobservable. We can follow van Fraassen in leaving it to science to determine

just what is and what is not observable. But there will always be much in any seientific theory that transcends its observational base, whatever that base is? ideas about the workings and nature of the entities observed, and about processes and forces that are not even in principle observable, and it is this much that the realist is concerned to assert, while the anti-realist would prefer to suspend

2 Cf. his 'Replies to Critics' in The Philosophy of Karl Popper, edited by P. A. Schilpp, La Salle, Open Court, 1974, pp. 1192-3.




judgement (probably urging that such suspension is advisable in the light of

history). Popper is a realist, who believes that nearly all our theories are false, that

success at the empirical level theory is no guarantee of a theory's truth at the level of its explanatory models (including any postulated unobservable entities), and that where a theory proves its mettle is at the hard cutting edge of its testable

predictions. Van Fraassen expressed surprise at the possibility of a realist who was not prepared to give some high degree of probability in the sense of positive belief to his theories. What I am suggesting is that it is hard to see what Popper's realism amounts to regarding the untestable core of theories. The actual demand of his methodology for theories that are 'empirically adequate', to use van Fraassen's phrase?that is for theories which make testable predictions that

survive testing. But like van Fraassen he will draw no conclusions from the

empirical adequacy of a theory as to the truth or reality of what other things a

theory states. He says that a scientific theory is an attempt to describe the real

world, but all we can know about its success or failure in its description of the

real world is if it fails, or is empirically inadequate. From an empirically inadequate

theory we learn that the world cannot be as it says; from a theory that is empirically

adequate we can if we wish continue to picture the world in its terms, but only provisionally. Although from both adequate and inadequate theories, we may make lots of unsuspected discoveries at the level of observation, we can never in

sum learn what the world is really like behind the phenomena. What then does

Popper's realism amount to?

According to van Fraassen, what the realist is always after is something

underlying and bringing about observable regularities. The idea is that we can

explain brute regularities in our experience by seeing or discovering what goes on behind the phenomena. For the scientific realist, explanation is characteristically 'the explanation of the known by the unknown', in Popper's phrase (RAS,

p. 133). Of course, as van Fraassen points out, and Popper admits, such

explanations will themselves end in further regularities at the level ofthe unknown, themselves in need of explanation. Popper points further (RAS^p. 149) to what

he calls Newton's problem: the reason for the basic structural properties themselves, the laws of nature. Won't we have to accept these regularities as simple givens, not further explicable by postulating further unknown causes? The realist, then, can be seen as having the same problem as the nominalistically-minded empiricist, and an additional one to boot. Both are faced with sets of regularities in the

physical world, which they cannot explain. The realist is faced, in addition, with

belief in sets of unobservable entities (forces, propensities, mysterious particles our instruments give us no direct access to, and the like), justification for belief

in which appears to rest on the weak argument from the alleged explanatory

power ofthe theories which postulate such entities, although when we come down

to it, this explanatory power consists in no more than empirical adequacy, or

confirmation of the theory's testable consequences. At least, this is all the reason

we are given by Popper for accepting the existence of any entity whatsoever. As

he thinks all observations depend on universal theories, the only reason he can

have for thinking that there is a glass of water in front of him when there is, is

that certain theories that imply such a thing have not yet been falsified.

One could, of course, reject this 'theory-led' account of common-sense



460 Anthony O'Hear

observation, and one would, I think, be right to do so. As Hume put it, "tis vain to ask, whether there be body or not? That is a point which we must take for

granted in all our reasonings'. As countless examinations of Cartesian scepticism, not least Wittgenstein's in On Certainty, have tended to show, all our thought and talk about the world are bound up with the assumption that the world is full of things like glasses of water, tables, dogs, and so on. No doubt our evolution, cultural and biological, has something to do with this givenness to us of body, and though we should be wary of actually basing any anti-sceptical argument on this evolutionary fact, it is plausible to think that the cause of our being right about the world of common-sense experience is our evolutionary development. But, by the same evolutionary token, we have no reason to suppose that our minds are well adapted to the small or the large world outside our common-sense

experience, and reason perhaps to think that they are not. What I am suggesting is that a naturalistic approach to human knowledge might suggest a robust realism regarding the observable realm and a healthy anti-realism regarding the

unobservable, something like van Fraassen's constructive empiricism, in which one does not believe that all aspects of acceptable theories have corresponding counterparts in reality, and that we might do well to remain agnostic on such

things as space-time, elementary particles, fields, and alternative possible states of affairs.3

Would Popper really disagree with this last suggestion? After all, he does not think we should believe in the content of acceptable theories, and his notion of corroboration (= survival of tests) could be seen as an analogue of van Fraassen's

empirical adequacy. The Postscript, though, is supposed to be the long-awaited work where the metaphysical elements of science are accorded their true role in

science, following the purely inspirational role accorded to metaphysics in the

Logic of Seientific Discovery:

The various ideas and hypotheses (of science) might be visualized as particles suspended in a fluid. Testable science is the precipitation of these particles at the bottom of the vessel . . . Ideas previously floating in higher metaphysical regions may sometimes be reached by the growth of science, and thus make contact with it, and settle. Examples of such ideas are atomism; the idea of a single physical 'principle' or ultimate element (from which the others derive); the theory of terrestrial motion (opposed by Bacon as fictitious); the age-old corpuscular theory of light; the fluid-theory of electricity (revived as the

electron-gas hypothesis of metallic conduction). All these metaphysical concepts and ideas

may have helped, even in their early forms, to bring order into man's picture of the world, and in some cases they may even have led to successful predictions. Yet an idea of this kind acquires seientific status only when it is presented in falsifiable form . . .4

A number of features of this passage are worth remarking, which is why I have

quoted it at length. Metaphysical ideas are not in themselves testable. A seientific

theory is one which leads directly to testable (i.e. observable) consequences (but remember that for Popper even seientific theories which survive testing remain

highly uncertain, particularly regarding the elements in them which are not subject to direct testing). When a seientific theory is eliminated through failing tests, what is actually eliminated? Presumably not the higher-level metaphysical elements that inspired it, because these are not in themselves testable. They could perhaps

3 Cf. The Seientific Image, p. 202. 4 Hutchinson, 1959, pp. 277-8.




reappear in a new guise as elements of a future world-picture, as Popper himself stresses in his discussions of theories of matter. What metaphysical ideas can do is to help us to bring order into our thinking about the world?determining for us a form of description, as Wittgenstein put it in the Tractatus (6.341)?but in

adopting one form of description rather than another, we cannot on Popper's terms conclude anything directly about how the world is, just because in themselves the ideas cannot be directly matched with reality, even for purposes of falsification. For example, what Popper calls the clockwork theory of the world?Descartes' idea that the essence of matter is identical with its spatial extension?was not in itself falsified by the failure of Newton to account for gravity in terms of bodies

acting on each other by contact of some sort; Newton's failure to find any contact in gravity, and his subsequent postulation of forces active between bodies looks

very much like the substitution of one form of description for another. It is just because the sources of these forms of description are at root

metaphysical that they escape scientific proof or disproof, and are bound to do so. No doubt we need metaphysics to elaborate forms of description?to bring order into our world-picture, as Popper puts it?but the metaphysics will always escape the test of a direct confrontation with reality. To say that, none the less, one regards the metaphysics as describing the real world is, in the absence of any check on the description, to say very little. Does the Postscript add anything to the evaluation of metaphysics in The Logic of Scientific Discovery? I must confess that I am unable to see that it does.

Some of the arguments in favour of realism in the Postscript are arguments against subjectivism and idealism per se. They cut little ice against a combination of realism at the observable level and anti-realism at the metaphysical level. The

arguments against instrumentalism (theories nothing but instruments) would not cut against a view according to which theories are regarded as more than instruments?as important and influential forms of description?but as less than the literal truth.

In the inspiring 'Metaphysical Epilogue' at the end of the Postscript, we are shown how metaphysical research programmes are indispensable for science, but not that any of them are literally true or demonstrably false. According to the

Metaphysical Epilogue, 'metaphysical' research programmes determine in the mind of the scientist what forms explanations can take, as well as direct his mind to certain empirically soluble problems as pressing. In the absence of such a

background, it is difficult to see any large-scale empirical enquiry having any sort of direction at all. It is true that under the direction of certain metaphysical ideas

empirical discoveries are made?discoveries which, historically and conceptually speaking, could not have been made under previously acceptable metaphysical systems. But as van Fraassen points out, this demonstrates no more than the

greater empirical adequacy of some of the theories that follow from the ideas; it does not provide an argument for the truth of the present world-picture,5 nor indeed would it provide a strong argument for the reality of those elements in corroborated theories which transcend the empirically accessible, wherever that line is currently drawn in science.

In his 'Metaphysical Epilogue', Popper outlines the history of the theories of

5 Cf. The Scientific Image, p. 82.



462 Anthony O'Hear

the nature of matter from early Greek times up to general relativity and quantum theory. He describes the passage from Descartes through Leibniz to Kant and Boscovich in some detail, concluding that we can see there how 'metaphysical speculations proved susceptible to criticism' and that this discussion was 'inspired by the wish to understand the world' and 'the conviction that the human mind can at least make an attempt to understand it' (QTSP, p. 172). But the criticizability of metaphysical speculations does not by itself show us that by means of them we can penetrate to knowledge of a level of reality deeper than the appearances. The anti-realist can agree that certain specific forms of description, such as those

admitting forces, lead to simpler accounts of the phenomena we have access to than others, say, forms of description which admit of no action at a distance. But he will insist this fact in itself shows neither that we should believe in forces nor that we should disbelieve in a Cartesian plenum with no action at a distance. The most that would be shown by any empirical results favouring one view as opposed to the other is that a specific form ofthe one doctrine is empirically more adequate than a specific form of the other.

Popper himself is in a strange way ambivalent here. He wants us to think of science as penetrating the secrets ofthe world, having a depth to it that non-realist accounts of science deny, and a lot of his rhetoric is aimed at reinforcing this

uplifting view of science, as an adventure of the human spirit, probing beneath the surfaces of phenomena. On the other hand, he knows as well as anyone that we never have any reason to believe that seientific speculations beyond the observation of entities are true. He thinks that sometimes we can see that they are false, however. But here he may be faced with a dilemma. We may be able to show that empirical theories are false, or empirically inadequate, but the

metaphysical-speculative elements of science resist empirical falsification (or they would not be metaphysical). So the speculative (i.e. non-testable) parts of science remain resolutely non-empirical. Even if they suggest the form of empirical theories, it is the empirical theories and not the underlying metaphysics that are

subjected to empirical testing. But what does it mean to say that metaphysical speculations uncover the secrets of the real world, if we can never know whether

they do or not. Is this simply a misleading way of saying that they sometimes lead

people to carry out empirical investigations, even though those investigations never establish either the truth or the falsity of the metaphysics?

I said just now that Popper was aware that we never had good grounds for

believing in the truth of seientific speculations. He himself actually uses the

argument from the potential infinity of competing theories compatible with any empirical evidence whatsoever to bring home this point.6 As far as metaphysical and seientific theorizing goes, empiricists of an anti-realist stamp would say that

Popper is quite right. Where they would disagree with Popper is in his attempt to tar the gathering of empirical evidence with the same fallibilist brush as theory. This is, as I remarked earlier, due to Popper's questionable belief that the

acceptability of observations depends on the acceptability of universal theories, and that we never have reason to accept the truth of observation reports independently of the truth of relevant theories. Perhaps here too, as so often, Popper would wish to have it both ways. He speaks of the physically real as what

6 Cf. The Logic of Seientific Discovery, p. 419.




can be kicked and kick back, and postulates the reality of photons on such

grounds, along with tables, chairs, and human bodies (QTSP, p. 84). But, of

course, nothing is what it seems in Popper. Being kicked by a photon or a body would nevertheless be an interpretation in the light of a theory, etc, etc. (cf. RAS, pp. 92-103).

Popper argues (RAS, p. 22) that it is possible to give reasons for proposing specific hypotheses and submitting them to critical discussion which are not the same as reasons for accepting them or believing them or thinking them justified. The reasons Popper is thinking of here are reasons which show that our favoured

hypothesis solves problems which its rivals cannot solve, and he thinks that such reasons can show that a particular hypothesis is a closer approximation to the truth than a rival. With this our empiricist about observation who is anti-realist about theory could, I think, agree. Success in problem-solving in science is for

Popper tied down to the successful survival of severe tests, at least as a necessary condition. Einstein's theories solve problems better than Newton's because they do better on the empirical evidence, especially on evidence which would, on

pre-Einstein grounds, be surprising. So, if this is so, Einstein's theories get nearer to the truth than Newton's. But the sense in which they get nearer to the truth is just the sense in which they do better on predictions, are more accurate and

far-ranging, etc. Leaving aside (which perhaps we should not do) Popper's problems with the justification of empirical evidence, Popper does, then, have a reason for saying that a theory that solves problems better than a rival is closer to the truth than that rival, because he would not and could not say that an

empirical theory that was not more adequate to the empirical evidence was a better solver of problems than its rival. But he has no reason and has given no reason for saying that a theory that solves problems better than a rival is closer to the truth in any other way, in particular that it is closer to the truth about the world at points that are not empirically scrutable. What, then, is the cash value of his realism about theory, and why is he so concerned to assert it?

That he is adamant about his realism?and what may prove a test case for that realism?comes out in considering his propensity theory of probability. Whatever we say about the observability of molecules or electrons, propensities are, like

forces, inevitably going to be unobservable. Probabilistic or statistical theories

are applied in areas where precise prediction is impossible, and where we are

unable to see individual objects of particular types as behaving in anything but

chance-like or random ways. Yet it appears that populations of such randomly

acting individuals are assimilable to predictions of a probabilistic kind. We find

that the relative frequencies of the various different outcomes of random events

tend to become stable over long runs. Sequences of individually random events, such as throws of a die or decay of radioactive particles, manifest empirically observable and testable regularities. Complete ignorance about the outcome of a

genuinely random event (the next throw of a die) is not only consistent with, but

actually entails predictability within a whole sequence of such events, providing

they are truly random and the sequence long enough. What Popper calls the

fundamental problem of the theory of chance is 'the seemingly paradoxical inference from the unpredictability and irregularity of single events to the

applicability ofthe rules ofthe probability calculus to them'.7

7 The Logic of Scientific Discovery, p. 188.



464 Anthony O'Hear

Although some philosophers have regarded any probabilistic statement, to the

effect that, say, the next throw of the die has a one in six chance of landing on

six, as a purely subjective confession of ignorance, Popper has always regarded

probabilistic theories as describing objective reality, and capable of empirical corroboration. Thus, for example, a long series of tests with a given die may

empirically corroborate our initial hypothesis regarding the turning-up of a six

on any given throw as ?. At the end of our series of throws we still estimate the

probability of six landing as \, but, contrary to a purely subjective interpretation of this statement as if it were simply a register of our ignorance or degree of

partial belief concerning the next throw, it seems we should regard our original

hypothesis as a statement about states of affairs in the real world rather than

about our beliefs, and one that our tests have confirmed. The most familiar interpretation of probabilistic hypotheses as being primarily

about the real world and not merely as referring to the strength of belief we might have in the occurrence or non-occurrence of various events before they happen is the so-called frequency theory, to which Popper himself initially adhered. On this view, a statement about the chances of the next throw being a six being \ is

to be understood as a statement about the proportion of sixes turning up in some

sufficiently long sequence of throws. It says, in other words, that in a sufficiently long sequence, one-sixth of all outcomes are or ,will be a six. The frequency theory has often been criticized for failing to deal satisfactorily with statements about single events. For example, one would be inclined to say that the next throw of the die has a \ chance of being a six, as a categorical truth, quite independent of any long sequence of throws with the die, which may not in any case take place. The frequency theorist may respond to this by invoking the notion of virtual sequences: sequences that do not actually happen, but which would happen in certain circumstances. Here, though, as Popper has stressed in

his criticism ofthe frequency theory, we have to be careful, because the probability of a given throw being a six may differ, depending on how we characterize the

sequence we are taking it to belong to. To see this, assume we have a very long actual sequence of throws with a loaded die, in which the probability of getting a six is i, but that we introduce into this sequence two or at most three throws

with a fair die. We will still want to say of these fair die throws, that the

probability of getting a six is ?, despite the fact that in the actual sequence to which they belong, the overall statistical frequency of a six is or is very close to

\. We will no doubt for our purposes wish to conceive the fair die throws as

properly belonging to a virtual (but non-actual) sequence of throws with the fair

die, in which the probability of a six is ?, rather than as a member of the actual

sequence of largely unfair die throws to which it also belongs. How are we so sure of this? Presumably because we believe that the conditions under which members of a sequence are produced (or generating conditions, as Popper calls

them) have some effect on the correct estimation ofthe relevant probabilities. And

this consideration appears to Popper to be decisive in favour of what he calls the

propensity theory of probability. The frequency theory has been criticized for its implicit operationalism?for

its tendency to interpret statements about the objective probabilities inherent in

actual individual set-ups in terms of the way such statements might be tested

(namely by examining frequencies of outcomes in sequences of comparable trials).




One can readily agree that Popper is right to stress the relevance of generating conditions to probability assessments, but can we move straight from this and a

general suspicion of operationalism to a propensity account of probabilities? What, in fact, are propensities? According to Popper, they are unobservable dispositional properties of the physical world, analogous to Newtonian forces, in that they are

responsible for observable effects, but different from Newtonian forces in that the effects they are responsible for are observable frequencies in repetitions of

events, rather than individual events (cf. RAS, p. 351). Indeed, it is possible to

regard Newtonian forces as the limiting case of probabilistic propensities, limiting in that a given force in similar circumstances always and predictably produces the same effect. Popper also says that he proposes to interpret 'the objective probability of a single event as a measure of an objective propensity?the strength of the tendency, inherent in the specified physical situation, to realize the event? to make it happen' (RAS, p. 395). So propensities are tendencies present in

physical situations to make things happen. The concept of a propensity is, as he

says elsewhere, an 'indeterministic generalization of an anti-Humean (i.e. realistic) view of causes'; they are physical realities, like forces, causally operative in

producing effects. To this view of propensities, I can only repeat the criticism D. H. Mellor and

I, following Mellor, have made elsewhere.8 Regarding propensities as forces makes it very hard to see how a strong propensity (for example the 60 per cent propensity of a biased coin to land heads) is ever overcome by a weak one (its 40 per cent

propensity to land tails). If there were two competing forces in a given situation, surely the stronger would always win. If, on the other hand, in speaking of

generating conditions as having propensities to produce specific frequences of effect in long sequences one is thinking of the propensities as causes that are only intermittently and in specific instances unpredictably effective, it is hard to see how talk of propensities adds anything to the observation that such and such

frequencies of heads as opposed to tails are observed to occur. To the empiricist, propensities as intermittent forces will inevitably look like some virtus dormitiva invoked ad hoc to explain the distribution of frequencies in classes of happenings. The connection between Popper's invocation of propensities and his realism is

this. Realism in science attempts to explain observable regularities by appealing to underlying and often unobservable structures. Probabilistic theories assert the

existence of predictable and objective regularities in distributions of frequencies. So the realist will want to say that there is something producing these regularities, namely propensities inherent in things or set-ups of various types to produce them. But one wonders what type of explanation is gained here by talk of

propensities, beyond saying that situations or structures of given types do regularly

produce frequency distributions of various sorts. D. H. Mellor, who has elaborated

his own version of the propensity theory, speaks of propensities as 'characteristics of things warranting conditional expectations of the future',9 and likens talk of

propensities to talk of dispositions. But unless one thinks of propensities in causal

terms, what is being said when it is said that this coin or this die in such and

8 Mellor in The Matter of Chance, Cambridge University Press, 1971, p. 158; O'Hear in Karl Popper, London, Routledge & Kegan Paul, 1980, pp. 156-7.

9 The Matter of Chance, p. 169.



466 Anthony O'Hear

such a set-up have propensities of various sorts? Do they have anything real, or exert any real force, or by talking in this way are we simply saying that they are individuals belonging to sequences defined in terms of their 'generating' conditions, which because of their similarities to other observed sequences we suppose will manifest various regularities? Is there any difference between this and some form of frequency theory? The only observably accessible facts are those recorded in actual frequencies. The real problem seems to be not that the frequency theory may be tainted with operationalist overtones but that the propensity theory postulates forces or tendencies of a quite mysterious sort. In particular, they are forces or tendencies present in individual things or set-ups, but which, without

being different in themselves in a class of similar cases yield different results in different individual cases. So my objection to propensities is not simply an anti-realist suspicion of forces. It is that the propensity theorist, unlike the

proponent of forces, gives no idea of how they work in the individual case; no

predictibn follows from a propensity statement about the next throw of a given die, but only about frequency distributions in sequences of throws in repeatable conditions.

Popper claims that the propensity theory, 'metaphysical' and 'occult' as

propensities are, receives some sort of empirical corroboration from quantum theory, but I must confess that I am unable to see this.

Popper, as is well known, defends an objectivist and realistic interpretation of

quantum physics, against the subjectivism and instrumentalism one often finds in

quantum theorists. In his view, the objects quantum physics mentions exist, and

they have definite physical properties; neither they nor their properties come into existence as a result of observer interaction. Quantum Theory and the Schism in

Physics, which includes the previously published 'Quantum Mechanics Without "The Observer"', shows that we do not need to believe that our own observing activity actually brings about definite states in systems which were previously somehow fuzzy, indeterminate, or non-existent, once we realize that the theories of quantum physics are statistical. It is not that single particles or systems have

spreads of properties or wave-like qualities which are somehow made determinate

by our measuring of them. It is rather that the theories in question do not allow in all cases for precise predictions and that measurement can sometimes make

precisely known what not formerly precisely predictable. We do not need to say that our acquisition of information in itself brings about a collapse of a wave

packet or a state vector. Popper illustrates his point by drawing an analogy with the behaviour of a ball on a pin-board, on which the ball is equally likely to pass to the left as to the right of a given pin. Before the event the ball's going to the left may be said to have a probability of j, and our theories may allow us to calculate nothing more precise than this. After the event, the probability of the ball's going to the left will, trivially, be either o or 1 depending on which way it has gone, and we may, by observation, have established which it is. But it would in this case be simply a loose way of implying that the probability of the event is being looked at from two different points of view to describe its actually going to the right as a change in its probability distribution, and quite misleading to think that of our observing its going to the right as actually leading to a 'collapse' of the original wave packet. Clearly in this case our observation has had no effect on the course of events, but has simply measured the probability of an event from




two different points of view, first its probability before it has happened and then after it has happened. Popper believes that Heisenberg and his followers have no more reason than a pin-board observer to think of a distant observer measuring the position of a photon as exerting some kind of action on it, so as to reduce its wave packet (cf. QTSP, pp. 74-8, 86-9).

To this commonsensical stand against some of the more bizarre outgrowths of

quantum physics, Popper wishes to add the propensity theory of probability. Let us allow that quantum physics is irreducibly statistical: that is to say, its theories cannot in many cases allow for precise predictions of individual events. The

question then arises as to how such an irreducibly statistical theory is to be

applied to single cases. It is this problem that the propensity theory is supposed to solve, and to do so by speaking of the tendency repeatable experimental arrangements have to produce statistically testable frequencies of various sorts

(cf. QTSP, pp. 79-80). Thus on a pin-board propensities for balls to follow

particular courses are generated by the various positions of the pins, and these

propensities would change if we removed a pin. As Popper puts it, 'If one ball rolls down, there will be many pins which it never touches. They do not influence the ball. But they influence the propensities inherent in the experimental arrangement: the propensities would change if these pins were shifted or removed'

(QTSP, p. 153). Imagine a ball which in fact goes down the left-hand side ofthe board. Prior to its going down, it might have had a propensity of, let us say, 0.1 to hit some particular pin on the right-hand part of the board. Now, if we had removed some of the right-hand pins close to the pin in question, this propensity might have been reduced to 0.05. So, it is claimed, events distant from and not related to what actually happens can change the propensities inherent in what

actually happens, propensities which are present in some way in every actual

event, even though they may not be manifested in any way in many of those events. It is in this way that talk of propensities is supposed to apply probability theory to single cases, but the pin-board case gives no compelling reason for not

regarding a propensity as simply an abstraction from observed frequencies, rather than something physically real in every situation. In this case, it would appear to be quite arbitrary whether we say the reducing propensity of our left-moving ball to execute the manoeuvre on the right of the board was something really there when it began rolling, or simply an oblique way of referring to the frequencies of various courses in sequences of pin-ball movement. But Popper's use of

propensities to 'explain' the two-slit experiment reveals the full extent of his realism in their regard, and, I think, casts some doubt on the explanatory power of his whole approach.

The problem posed by the two-slit experiment is that a photon or an electron

passing through a slit in a certain screen appears to be influenced in its subsequent behaviour by the mere fact that another slit on the screen is open as opposed to

shut, even though it goes nowhere near the second slit. Popper interprets this

phenomenon by claiming that the particle is uninfluenced by the opening of the second slit and that 'what the (second) slit influences are the propensities of the

particle relative to the entire experimental arrangement, not the particle itself: the

propensities for reaching the one point or the other on (a further) screen' (QTSP, p. 153). But this is quite different from the way the propensities are altered in the pin-ball case, in which the removal of pins has no effect on the actual courses



468 Anthony O'Hear

of balls that pass nowhere near them, but only on the earlier propensities they had to take certain unactualized courses. Popper claims that the two-slit experiment and other quantum phenomena show that propensities are physically real (cf. QTSP, p. 84), but the suspicion remains that they may be no more than ad hoc devices to explain a phenomenon that remains bafrling and which has led physicists to talk of photons as having the character of both particles and waves. In Popper's view, what we have are single particles that have propensities to take various courses after passing through a slit, and it is because people have misread these

propensities as being part of the actual physical behaviour of single particles that

they have thought of them as having the character of waves. The equations which determine the relevant propensities have a wave-like character, not the particles themselves. What the pin-ball analogy shows is that different experimental arrangements yield different propensities, so that we can accept that opening or

closing the second slit will change the propensities of all particles approaching the screen to hit another screen beyond the first one, even of those that do not

go near the second slit. But this is not the real problem with the experiment, which is that opening the second slit appears to alter not just the propensities of

particles which actually go through the first slit, but their actual courses. And

this, of course, is not replicated on pin-boards. Moving pins on boards would not generally affect the course of balls that do not go near them. Bartley, Popper's editor, says that this objection (which is due largely to Feyerabend), misses the

point because 'Popper was not attempting to explain interference with the

pin-board example'.10 If this is so, then how can it be that the two slit experiment 'cannot be understood without difficulty except perhaps in terms ofthe propensity interpretation' (QTSP, p. 151), for the whole problem raised by the experiment is the problem of actual interference, not change in propensities? We can, if we

like, say that opening or shutting the second slit changes the propensities of the

experimental arrangement so as to cause the particle to reach a particular point on the further screen (and the distinction between this and actually influencing the course of the particle is extremely fine), but how are we to conceive an alteration of propensities that affects the actual course of a particle? What is in the opening of the second slit that underlies that or brings that about? In the absence of answers to such questions, does appeal to propensities here add

anything in the way of explanation to the problem we already have, which still seems to be the old problem of interference? Just because the original problem remains untouched by the propensity theory, it is impossible to accept Popper's claim (RAS, p. 360) that the theory the two-slit experiment provides a crucial corroboration of the propensity theory against purely statistical interpretations of

probability. But the fact remains that in physics and everyday life we make use of

probabilistic theories, which regard individual events as random in the sense that different results follow from apparently identical set-ups. To say that such set-ups have propensities to produce individual outcomes is, I have argued, not to say much more than that they simply do, but even this claim?that different results

10 Bartley in Part Two of his 'Critical Study of The Philosophy of Karl Popper* in Philosophia, 1978, p. 695; Feyerabend in 'On a Recent Critique of Complementarity', Philosophy of Science, 1968, pp. 309-31, and 1969, pp. 82-105.




can emerge from identical starting-points?is one that will be found repugnant to many people. For these people?determinists?probabilistic theories are always indications of our ignorance, that in certain respects we do not know enough about the factors which cause events or the laws which determine them. If we

did, we would see that two similar situations never produce different results and that difference of result is always due to difference of cause. This was very much

Popper's own view in The Logic of Scientific Discovery (p. 212), where he rejected the idea that the outcome of an event may hang in the balance in an indeterministic

way. But the theory of propensities of situations tending to produce a variety of

effects, only one of which is actually realized, is just such an idea, and part of

Popper's later commitment to a world-view that has room for as yet-undetermined outcomes.

The second part of the Postscript is subtitled An Argument for Indeterminism and in it, among other arguments, one can find a reformulation of Alfred Lande's

argument to the effect that statistical results or theories cannot be derived from classical deterministic assumptions. The reason for this is that a statistical effect, such as the one envisaged by Lande, in which balls fall apparently randomly over a steel blade but in a 50:50 ratio overall, requires an absolutely incredible chain of assumptions if one is going to explain it by appeal to deterministic premisses. For each ball's fall will then be brought about by long chains of deterministic causes (which result in all the fluctuations that make it go to left rather than to

right), so arranged in the remote past that all the causes producing all the falls of all the balls have tended, through some pre-established harmony, to produce a sequence of falls that was at once random yet in the 50:50 ratio of left to right falls. According to Popper if the determinist accepts, as he surely should, that the 50:50 result has something to do with the initial experimental conditions, he is reduced to proposing an 'irreducible and miraculous statistical distribution of the initial conditions' (OU, p. 103) to explain why the random sequence has the overall regularity it does.

Lande's argument has an undoubted fascination, but I am not clear why it is

supposed to refute determinism. The determinist can surely allow that the outcome of events may be subject to thousands of small variations of initial conditions.

Why should these small variations not combine to produce sequences of outcomes that are statistically random at the individual level, and regular at the level of whole sequences? Popper takes the fact that a constant variation in one of the initial conditions, such as the angle of the blade, will change the overall ratio of

falls from 50:50 to say 40:60 as a further problem for the determinist, but this is

surely just what he would predict. The change in the position ofthe blade cancels

out the effects of a number of the little air currents that would previously have

caused balls to fall to the left. In the limiting case, a change in one condition may be so great that no fluctuations in other conditions cause any balls to fall to one

side, and all appearance of randomness among individual falls goes; is Popper

going to say that this example provides a problem for the determinist? This would

surely be implausible, for randomness has now been eliminated, but if he does

not, why do the other cases present problems, for there is a continuity between

the 100 per cent case and the ones where 50 balls fall to the left and 50 to the

right? All can be conceived as the outcomes of variations in initial conditions.

Where these variations are slight but still big enough to have a potential effect



470 Anthony O'Hear

on outcomes, why should the process by which the outcomes are balanced not

display a certain randomness in the way the balancing is achieved? Talk of a

pre-established harmony between the remote causes of initial condition suggests that the determinist is assuming that the balls falling over the vertical blade are

trying to achieve a 50:50 ratio in their falls. The determinist would not assume

this, but rather conclude from an observed 50:50 split in an otherwise random

sequence that the various factors in the situation are pretty evenly balanced in their effects on the outcomes, so that they cancel each other out in the long run. I am not clear why this sort of observed pattern in events is any more of a problem for a determinist than any other pattern. Events that are individually determined can combine to produce all sorts of outcomes in all sorts of patterns, and changing the determinants would naturally, from a deterministic point of view, change the

patterns. Much ofthe argument of The Open Universe concerns various aspects of human

knowledge and the impossibility of prediction of our future states of knowledge. Here I think that Popper is largely correct, if only because predicting now that we would know in the future would entail, contrary to our premisses, that we know it now. But I am not clear that this and similar demonstrations of the

impossibility of self-prediction show that our mental states are not determined and even predictable by others, rather than that there are certain limits to our

knowledge of them. One other line of argument on determinism which Popper advances deserves mention here. It is that it is always irrational to accept that universal determinism is true, because if it were true then one's acceptance of the thesis would also have been determined, and this is inconsistent with one's

accepting it on rational grounds (cf. OU, pp. 81-5). Popper believes that if our mental states are determined, by chemical or neurophysiological laws, say, then there is no difference between brainwashing and rational learning. Each mental state of ours would be present in us because it had been determined to follow its

predecessors, and this leaves no room for the operation of rational processes in its genesis. Now while it is true that the determinist will think of all one's beliefs and arguments as determined, perhaps at the neurophysiological level, it is not

necessarily true that he cannot make some sort of distinction between brainwashing and rational argument. He could identify and distinguish different types of routes to belief according to their power to produce true beliefs, and even examine his own past or present beliefs in the light of what emerged from this process. Of

course, he would admit that his coming to regard certain beliefs as true and his

engaging in the examination of types of belief formation were determined, but this would not in itself affect either the truth of the beliefs or the soundness of his examination, nor would it mean that the processes that underlay his mental

activity were not rational or truth-preserving. A determinist could certainly make the relevant distinctions and believe, even for good reasons, that some of his

beliefs, including that in determinism itself, had been brought about in him by means that yielded their truth.

Popper says of The Open Universe that it is *a kind of prolegomenon to the

question of human freedom and creativity, and makes room for it physically and

cosmologically' (pp. xxi-xxii). Indeterminism at the physical level is important for him because it leaves room for human freedom and creativity. Equally, it is

important for him to show that determinism is an unacceptable doctrine, quite




apart from any reference to theories in current physics. Furthermore 'we live in a universe of emergent novelty; of a novelty which, as a rule, is not completely reducible to any ofthe preceding stages' (OU, p. 162). Clearly the most significant of these novelties, humanly speaking, is the emergence of free, creative human

beings. There is no doubting Popper's humanity and much to admire in it and in his concern to emphasize the need to criticize and monitor our exercise of our freedom. For example, in two places in the Postscript, he warns against the nuclear bomb and the peaceful use of atomic energy and the problems of 'atomic wastage' (QTSP, p. 199 n.; RAS, p. 260). He says (in 1953, remember) that in the long run the consequences of the so-called peaceful use of atomic energy may be even worse than those of the nuclear bomb. Antony Flew appears to regard these

warnings as something of an aberration in Popper, a dated side remark,11 but I do not think this is so. They are, in fact, an aspect of Popper's hostility to instrumentalism. Morally, talk of command over nature repels Popper: 'this

command, this control, is apt to be self-defeating, and apt to enslave us rather than to make us free?if it does not do away with us altogether. And while

knowledge is worth dying for, power is not. (Knowledge is one of the few things that are worth dying for, together with liberty, love, kindness, and helping those who are in need of help.)' (RAS, p. 260). Science has become technical, instrumental and specialized and has estranged science from what ought to be its true users?'the amateur, the lover of wisdom, the ordinary, responsible citizen who has a wish to know'. With all this, one can express only agreement and

respect for Popper's attitudes. I feel, though, that Popper does not say enough about human nature. His

rejection of determinism and his emphasis on freedom leave room for something, but what they leave room for, he does not say. He has nothing on which to base his convictions about what is worth dying for, beyond very strong intuitions.

Why do creative beings have to be kind, one feels like asking. In asking this, one also feels a kind of unworthiness. Popper's moral convictions pervade and shape his thought, including, I am suggesting, his hostility to instrumentalism, his

commitment to realism and to the seientific game. It is the moral force of his vision

and his philosophy that makes it so attractive and, to many, so liberating, and a

large part of why so many scientists respond to Popper and his writings in a way

they would not respond to those of any other philosopher of science. But it is

perhaps for this reason above all that we must submit his arguments to the sort

of scrutiny that would show just what they do and what they do not establish.

University of Bradford anthony o'hear

11 Cf. Flew's review of Popper's Postscript in Philosophical Investigations.



realism and the aim of science.by karl popper; w. w. bartley;the open universe: an argument for...

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