Logic, Thought, and Action 9

Chapter 9 MICHEL GHINS ON THE EMPIRICAL VERSUS THE THEORETICAL∗ Bas C. van Fraassen Princeton University.

Abstract

1.

Michel Ghins and I are both empiricists, and agree significantly in our critique of “traditional” empiricist epistemology. We differ however in some respects in our interpretation of the scientific enterprise. Ghins argues for a moderate scientific realism which includes the view that acceptance of a scientific theory will bring with it belief in the existence of all those entities, among the entities the theory postulates, that satisfy certain criteria. For Ghins these criteria derive from the criteria for legitimate affirmation of existence for any entities, the directly observable ones not being privileged in that respect. They are roughly that the putatively existing entity should according to the accepted theory manifest itself in our experience, and display a certain permanence and invariance. My disagreement on this topic derives from a larger difference concerning the relation between experience, existence, and theory.

Introduction

The empiricist tradition admits of a great variety of views and of diverse links with other traditions. This diversity is evident when I try to compare Prof. Ghins’ views to my own, and both of ours to others. We are both empiricists, or rather, trying to be (for neither of us is content with empiricism’s past; it is a matter of forging new stages for an old tradition). We are agreed in some of our critiques of “traditional” epistemology, including some items erstwhile beloved of empiricists. I will mention some of our agreements, and then draw attention to some of ∗ Commentary on M. Ghins, “Empirical versus theoretical existence and truth.” I wish to thank Michel Ghins for helpful conversations. This article appeared earlier in Foundations of Physics, 30 (2000), 1655–1661. It is reprinted with permission.

D. Vanderveken (ed.), Logic, Thought & Action, 175–181. 2005 Springer. Printed in The Netherlands.

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our differences. I would like to emphasize that for the most part I cannot argue the issues; I will simply display my different way of approaching them, as basis for future dialogue. One agreement is very clear: while we both wish to give a central role to experience in epistemology, we both reject the myth of the “given” and the phenomenalist views which elaborated on that myth. We are also agreed in our wish to respect the phenomenology of scientific inquiry. We share the hope for a truly non-foundationalist and yet empiricist epistemology.

2.

Separating the questions

Concerning existence and truth, I should like to separate questions of epistemology from questions of meaning, reference, and truth. Prof. Ghins writes: “These two conditions of presence and invariance constitute jointly the sufficient condition, the criterion, of existence. . . ”

The context makes clear that “presence” refers here to presence in experience, and that the two conditions are being presented as legitimizing affirmations or attributions of existence. That is: if I encounter something in experience, then I may legitimately assert its existence. The term “invariance,” characterizes the (putative) object to which existence is attributed. When Prof. Ghins discusses the reality of the electromagnetic field, he mentions its permanence and the invariance of certain of its properties. Should we think of this as meant to indicate a necessary condition of existence? This would take us outside the area of purely epistemological issues, to issues of ontology. But as I read him, I see this factor mentioned only in adduced grounds for legitimate affirmation of existence. Thus I think that we have here also to do with a partial criterion of legitimacy for assertion of (or belief in) the existence of something. So if I construe this rightly, we are not discussing a criterion of existence, strictly speaking, but a criterion of warranted or legitimate assertion, affirmation, or belief. The suggested epistemic principle (which may or may not be meant to extend to attributions of properties as well as affirmations of existence) is a sophisticated version of something like the idiom “seeing is believing.” Principles of this sort have indeed been associated with the empiricist tradition. I will discuss this subject further in the next section. In the meanwhile, at the risk of sounding overly pedantic, I would like to emphasize that, in my view, existence has nothing to do with experience, at least not in general. Nor does permanence or invariance. I would not

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accept any such considerations as bearing on necessary conditions for existence in general. They may bear on the sort of object we are considering: nothing can be a mountain, for example, or a dinosaur, or a horse, without being perceivable and persisting for an appreciable amount of time. This follows from the sorts of things mountains, dinosaurs, and horses are. Therefore it is true about any of them, existent or not. If it implies something about existing mountains (dinosaurs, horses) that is simply because an existing mountain (dinosaur, horse) is a mountain (dinosaur, horse). The same holds, it seems to me, for the counterfactual assertions implied by certain existence statements, about what we would perceive under different conditions. If you look at a horse from a different angle, you will see a shape predictably related to your first view, by a certain geometric transformation. This is not because it exists, but because it is a horse, and because our vision is thus and so, light is such and such, and so forth. Perhaps there are also entities which are vanishingly transient, one- or two-dimensional, invisible, intangible. . . I do not know; but the meaning of “existence” will not legislate on that question.

3.

Can we reject the epistemic principle?

Even if these remarks did no more than clear the ground for discussion, they serve to raise the question: what of the epistemic principle, apparently suggested here, for legitimate affirmation of existence? Now, as I see this, an affirmation of existence is an assertion, and so the principle must take the form: under the following conditions, one may legitimately assert [believe] that such and such is true. Is it really the case that if we perceive something and it displays a certain permanence in our experience (as well as some invariance in its properties as we or others inspect it from different angles), then we may legitimately assert that it exists? To me that question remains ambiguous, until we are told what may be substituted in the “it.” Are we to read this principle de re or de dicto? The former seems inappropriate, for it would amount to: If something is perceived by a person, etc., then that person may legitimately assert that it exists. To apply that principle in a particular case, the person would have to already believe that there was something s/he was perceiving, and I take it that “there is” means “there exists.” But I have even more difficulties with the de dicto reading, on which the “it” can, in effect, be a placeholder for a descriptive phrase. Suppose that burning is oxidation. Imagine now a person raised on the phlogiston theory, having much evidence for that theory, and as yet very

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little evidence to support the new rival theory about oxygen. This person encounters some fire [oxidation] and perceives that this phenomenon has some permanence etc. Is this person now entitled to assert or believe that oxidation exists (is taking place)? Is s/he not much more entitled to assert that phlogiston is escaping instead? We cannot disentangle questions about [belief in] existence from questions about truth. The example I just gave calls into question Prof. Ghins suggestion that a statement about ordinary observable objects can be called true on the basis of simple experiences. The same considerations would seem to me to bear on a criterion of truth in relation to our experience. Statements are true if what they say is indeed so, and false if what they say is not so; isn’t that pretty well the end of the matter? As I said, I am not so much arguing here as displaying a different way of thinking about the same issues, predicated (in my case) on a quite sharp separation between epistemology and semantics. As I see it, the main ambiguity in the philosophical notion of experience is between, on the one hand, what happens to us that we are aware of, and on the other hand, our immediate and spontaneous response to what happens to us. What happens to us, and which of the events that happen to us are noticed by us, those are factual questions whose answers depend on theory-independent factors. But how we respond –and here I include the very first, spontaneous response to those events, prior to any discursive thought– is clearly conditioned by the language in which we live. Any judgement involved in that response (such as “Lo! phlogiston escaping!”) always involves some implicit description of the event. This description is historically conditioned –and in general, theory-laden– to a very large extent. An accepted theory may be wrong. If we attend critically to our experience and we have the proper ration of epistemic luck, this falsity will manifest itself in the disappointment of expectations shaped by that theory. Until that happens, however, all those expectations may well be legitimate, warranted, entitled, rational, reasonable, what have you. The grounds adduced for them will be reports on our experience themselves shaped by that very theory, couched in its terms, and implying counterfactuals and predictions via that theory.

4.

Moderate realism

I shall leave myself open to suspicions of stone-walling or evasion if I do not reply to Prof Ghins’ main challenge, from one sort of empiricist to the other sort of empiricist that I wish to be. Prof. Ghins argues for a moderate scientific realism. If I understand him correctly, and if I may put it to some extent in my own terms, this means that acceptance of

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a scientific theory will bring with it belief in the existence of all those, among the entities it postulates, which satisfy certain criteria. These criteria derive from the criteria for legitimate affirmation of existence for any entities, the directly observable ones not being privileged in that respect. They are roughly, as we saw, that the putatively existing entity should manifest itself in our experience, and display a certain permanence and invariance in certain respects. While this is a little abstract, Prof Ghins’ example of the electric field, as discussed by Herman Weyl, makes it very clear: An objective reality can thus be conferred on an electric field when actual forces are experienced (condition of presence) and when a systematic variation of some properties is ascertained within the sequence of perceptions (forces). But some of the distinctions I made above may be brought into play here. That is perhaps easier with respect to the metric-gravitational field.1 Prof. Ghins writes: “Moreover, a spacetime geodesic is surprisingly easy to visualize: just let a pen drop on the floor, it will follow an inertial and extremal path in spacetime.”

Imagine now three people watching this experiment with the pen: a Stone Age primitive, a Newtonian, and one of our (sufficiently educated) contemporaries who believes in the reality of the metric-gravitational field. The third is indeed entitled to assert that he can, as it were, point to a geodesic line segment. The second is at least entitled to believe that he saw a pen drop; the first is not entitled to believe even that. Perhaps seeing is believing; and undoubtedly all three saw the very same thing (event); but they did not all see that the pen followed a geodesic.

1 The

example of the mouse has its intricacies, and is rather different, as I see it, from either the electromagnetic or metric field. Prof. Ghins suggests two hypotheses, each of which fits the findings in my kitchen. One of these implies the presence of one mouse doing many things, and the other implies the presence of many mice doing a little each. It is true that the findings would prima facie support either hypothesis. There are, however, various ways to construe the second hypothesis. If all those mice are real mice, and are as described by current biology, I would not consider the second hypothesis empirically equivalent to the first, for the observable phenomena would not all be the same. (The actually observed phenomena may be the same, if human observers are successfully evaded.) A kitchen with two mice in it is different from one with only one. If the hypothesis is instead of science-fiction mice, who are very transient, springing into and out of existence, there is also an observable difference, though of a different sort. Finally we may entertain a third construal on which the difference is real but not empirical, for instance if empirical mice are construed as sets or series of “time-slices.” Such empirically equivalent but “metaphysically” distinct possibilities are of course encountered in certain interpretations of quantum mechanics, e.g., in connection with the “problem of identical particles.” I would never wish to forbid theoretical recourse to anything, as long as it is logically consistent, but do not see acceptance of science as requiring a choice to believe in one rather than another of such empirically equivalent hypotheses.

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The reality of the event is not in question. Nor is there any question as to how this event should be classified relative to various theories. But that does not logically settle either how much of those theories is true, or how much we need to believe of them when we judge them adequate by all publicly applicable standards.

5.

Immoderate empiricism

Empiricism is often suspected of idealist leanings, and Prof. Ghins very clearly lays some of those suspicions to rest. He rejects phenomenalism, the myth of the given and all its ilk, removing the suspicion that he views reality as constituted by or constructed from experience. His moderate realism with respect to science is both genuinely moderate and genuinely realist. To put it in my own terms, if I may: this moderate realism entails that acceptance of science involves belief in the reality of all those entities among the ones it postulates that bear a certain relationship to what (according to science) can be experienced. In form at least this is very close to the “constructive empiricism” which I advocate. The difference appears when we ask about that “certain relationship.” How that question is answered will draw a line in the sand, so to speak, and constructive empiricism is less moderate: it reads “bear a certain relationship to” very strictly as “are among.” But as noted above, this close resemblance between the two positions occurs in a context which may harbor deeper disagreement, and thus qualify the resemblance. I see empirical science as a certain sort of enterprise, oriented to empirical success. To me, this orientation does not have a deeper or privileged basis, either in a connection between reality and experience, or in principles of warrant or legitimacy that confine rational belief to within certain bounds. We engage in an enterprise because we value the results it aims for and because we believe in its adequacy (or superiority to any rivals) as means to that end. There are other sorts of enterprise, distinct from empirical science, distinguished from it by their own aims and not by lesser or greater epistemic warrant. Am I skeptical of those non-scientific enterprises? I am certainly skeptical of certain forms of metaphysics, both traditional and analytic, and never more than when they purport to be extensions of science in the scientific spirit. On the other hand, I think that much of what we come to understand, know, or find out about ourselves, others, and the human condition is not within the domain of science at all, and the way in which we do so is not at all by means of the sort of “objectifying” inquiry proper to science. Science is a shining example of a cognitive

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enterprise with a clear and admirable ethic of inquiry. But to follow an example judiciously requires judgement. Quite possibly Prof. Ghins and I are in agreement on this. But with the emphasis on the distinctive aims of science must come a more nuanced view of experience. The historical character of science is to be taken into account, and the relationship between empirical science and experience –as well as the character of experience in general– is complex. As always, I would insist that what happens to us, what we observe and what we can observe, are all matters which are entirely independent of theory, whether learned, interiorized, or considered hypothetically. But the form of our response is not, and when we try to relate theory to what has shown itself to us in experience, we can only start from the language in which we spontaneously react, with the possibility of self-criticism (including critique of our own prior language and opinion) necessarily posterior to that stage.2

2 For

some elaboration of these brief comments, see my “From vicious circle to infinite regress, and back again,” D. Hull, M. Forbes, and K. Ohkruhlik, eds., PSA 1992, Vol. 2 (Proceedings of the Philosophy of Science Association Conference, Nov. 1992) (Chicago, Northwestern University Press, 1993), pp. 6-29.

III

PROPOSITIONS, THOUGHT AND MEANING