It is a pleasure for me to give this opening address to the Royal Institute of Philosophy Conference on ‘Explanation’ for two reasons. The first is that it is succeeded by exciting symposia and other papers concerned with various special aspects of the topic of explanation. The second is that the conference is being held in my old alma mater, the University of Glasgow, where I did my first degree. Especially due to C. A. Campbell and George Brown there was in the Logic Department a big emphasis on absolute idealism, especially F. H. Bradley. My inclinations were to oppose this line of thought and to espouse the empiricism and realism of Russell, Broad and the like. Empiricism was represented in the department by D. R. Cousin, a modest man who published relatively little, but who was of quite extraordinary philosophical acumen and lucidity, and by Miss M. J. Levett, whose translation of Plato's Theaetetus formed an important part of the philosophy syllabus.

A number of recent writers have argued that we should explain mental representation teleologically, in terms of the biological purposes of beliefs and other mental states.

A rather older idea is that the truth condition of a belief is that condition which guarantees that actions based on that belief will succeed.

What I want to show in this paper is that these two ideas complement each other. The teleological theory is inadequate unless it incorporates the thesis that truth is the guarantee of successful action. Conversely, the success-guaranteeing account of truth conditions is incomplete until it is placed in a teleological context.

Donald Davidson finds folk-psychological explanations anomalous due to the open-ended and constitutive conception of rationality which they employ, and yet monist because they invoke an ontology of only physical events. An eliminative materialist who thinks that the beliefs and desires of folk-psychology are mere pre-scientific fictions cannot accept these claims, but he could accept anomalous monism construed as an analysis, merely, of the ideological and ontological presumptions of folk-psychology. Of course, eliminative materialism is itself only a guess, a marker for material explanations we do not have, but it is made plausible by, inter alia, whatever difficulties we have in interpreting intentional folk-explanations realistically. And surely anomalous monism does require further explanation if it is to be accepted realistically and not dismissed as an analysis of a folk-idiom which is to be construed instrumentally at best. Some further explanation is needed of how beliefs, desires, etc. can form rational patterns which have ‘no echo in physical theory’ and yet those beliefs, desires etc. be physical events. To this end I propose to graft on to anomalous monism a modest version of functionalism.

During the war, I worked in aircraft design. About a year after D-day, an exhibition was arranged at Farnborough of the mass of German equipment that had been captured, including the doodlebug and the V2 rocket. I and a friend spent a fascinating two days wandering round the exhibits. The questions that kept arising were ‘Why did they make it like that?’, or, equivalently ‘I wonder what that is for?’ We were particularly puzzled by a gyroscope in the control system of the V2. One's first assumption was that the gyroscope maintained the rocket on its course, but, instead of being connected to the steering vanes, it was connected to the fuel supply to the rocket. Ultimately my friend (who would have made a better biologist than I) remembered that the rate of precession of a gyro depends on acceleration, and saw that the Germans had used this fact to design an ingenious device for switching off the engines when the required velocity had been reached.

When philosophers discuss the topic of explanation, they usually have in mind the following question: given the beliefs one has and some proposition that one wishes to explain, which subset of the beliefs constitutes an explanation of the target proposition? That is, the philosophical ‘problem of explanation’ typically has bracketed the issue of how one obtains the beliefs; they are taken as given. The problem of explanation has been the problem of understanding the relation ‘x explains y’. Since Hempel (1965) did so much to canonize this way of thinking about explanation, it deserves to be called ‘Hempel's problem’.

Are explanations in the social sciences fundamentally (logically or structurally) different from explanations in the natural sciences? Many philosophers think that they are, and I call such philosophers ‘difference theorists’. Many difference theorists locate that difference in the alleged fact that only in the natural sciences does explanation essentially include laws.

Hempelian orthodoxy on the nature of explanation in general, and on explanation in the social sciences in particular, holds that

(a) full explanations are arguments

(b) full explanations must include at least one law

(c) reason explanations are causal

David Ruben disputes (a) and (b) but he does not dispute (c). Nor does he dispute that ‘explanations in both natural and social science need laws in other ways, even when not as part of the explanation itself (p. 97 above). The distance between his view and the covering law theory, he points out, ‘is not as great as it may first appear to be’ (p. 97 above).

In what sense do the sciences explain? Or do they merely describe what is going on without answering why-questions at all. But cannot description at an appropriate ‘level’ provide all that we can reasonably ask of an explanation? Well, what do we mean by explanation anyway? What, if anything, gets left out when we provide a so-called scientific explanation? Are there limits of explanation in general, and scientific explanation, in particular? What are the criteria for a good explanation? Is it possible to satisfy all the desiderata simultaneously? If not, which should we regard as paramount? What is the connection between explanation and prediction? What exactly is it that statistical explanations explain? These are some of the questions that have generated a very extensive literature in the philosophy of science. In attempting to answer them, definite views will have to be taken on related matters, such as physical laws, causality, reduction, and questions of evidence and confirmation, of theory and observation, realism versus antirealism, and the objectivity and rationality of science. I will state my own views on these matters, in the course of this essay. To argue for everything in detail and to do justice to all the alternative views, would fill a book, perhaps several books. I want to lead up fairly quickly to modern physics, and review the explanatory situation there in rather more detail.

The corpus of physical theory is a paradigm of knowledge. The evolution of modern physical theory constitutes the clearest exemplar of the growth of knowledge. If the development of physical theory does not constitute an example of progress and growth in what we know about the Universe nothing does. So anyone interested in the theory of knowledge must be interested consequently in the evolution and content of physical theory. Crucial to the conception of physics as a paradigm of knowledge is the way in which physical theory provides explanations of a vast diversity of natural phenomena on the basis of a very few fundamental principles. A central problem for the epistemologist is therefore what is theoretical explanation in physics? Here we can get good insight from what Redhead has said (this volume pp. 145–54). Indeed one could agree with almost everything Redhead says and simply endorse much of his careful and extensive defence of the covering law account of explanation in the physical sciences at least as an ideal. However I shall, I fear, try the reader's patience by extending some of the considerations he introduced and raising those issues where we disagree, especially in the important area of statistical explanation.

In purporting to explain the occurrence of some event or process we cite the causal factors which, we assert, brought it about or keeps it in being. The explanation is a true one if those factors did indeed bring it about or keep it in being. In discussing explanation I shall henceforward (unless I state otherwise) concern myself only with true explanations. I believe that there are two distinct kinds of way in which causal factors operate in the world, two distinct kinds of causality, and so two distinct kinds of explanation. For historical reasons, I shall call these kinds of causality and explanations ‘scientific’ and ‘personal’; but I do not imply that there is anything unscientific in a wide sense in invoking personal explanation.

When I was first approached to read a paper at the conference from which this volume takes its beginning I expected that Flint Schier, with whom I had taught a course on the Philosophy of Biology in my years at Glasgow, would be with us to comment and to criticize. I cannot let this occasion pass without expressing once again my own sense of loss. I am sure that we would all have gained by his presence, and hope that he would find things both to approve, and disapprove, in the following venture.

In his recent book, Causation: A Realistic Approach, Michael Tooley discusses the following thesis, which he calls the ‘thesis of the Humean Supervenience of Causal Relations’:

(T) The truth values of all singular causal statements are logically determined by the truth values of statements of causal laws, together with the truth values of non-causal statements about particulars (p. 182).

(T) represents one version of the ‘Humean’ idea that there is no more factual content to the claim that two particular events are causally connected than that they occur, instantiate some law or regularity, and perhaps bear some appropriate non-causal (e.g. spatio-temporal) to each other. This is an idea that is tacitly or explicitly assumed in most familiar accounts of singular causal statements. For example (T) is assumed by many probabilistic theories of singular causal statements, by theories which attempt to analyse singular causal statements in terms of necessary and sufficient conditions, and, as I shall argue below, by David Lewis' counterfactual theory.

According to a causal model of explanation, we explain phenomena by giving their causes or, where the phenomena are themselves causal regularities, we explain them by giving a mechanism linking cause and effect. If we explain why smoking causes cancer, we do not give the cause of this causal connection, but we do give the causal mechanism that makes it. The claim that to explain is to give a cause is not only natural and plausible, but it also avoids many of the objections to other accounts of explanation, such as the views that to explain is to give a reason to believe the phenomenon occurred, to somehow make the phenomenon familiar, or to give a Deductive-Nomological argument. Unlike the reason for belief account, a causal model makes a clear distinction between understanding why a phenomenon occurs and merely knowing that it does, and the model does so in a way that makes understanding unmysterious and objective. Understanding is not some sort of super-knowledge, but simply more knowledge: knowledge of the phenomenon and knowledge of its causal history. A causal model makes it clear how something can explain without itself being explained, and so avoids the regress of whys, since we can know a phenomenon's cause without knowing the cause of the cause. It also accounts for legitimate self-evidencing explanations, explanations where the phenomenon is an essential part of the evidence that the explanation is correct, so the explanation can not supply a non-circular reason for believing the phenomenon occurred. There is no barrier to knowing a cause through its effects and also knowing that it is their cause. The speed of recession of a star explains its observed red-shift, even though the shift is an essential part of the evidence for its speed of recession. The model also avoids the most serious objection to the familiarity view, which is that some phenomena are familiar yet not understood, since a phenomenon can be perfectly familiar, such as the blueness of the sky or the fact that the same side of the moon always faces the earth, even if we do not know its cause. Finally, a causal model avoids many of the objections to the Deductive-Nomological model. Ordinary explanations do not have to meet the requirements of the Deductive-Nomological model, because one does not need to give a law to give a cause, and one does not need to know a law to have good reason to believe that a cause is a cause. As for the notorious over-permissiveness of the Deductive-Nomological model, the reason recession explains red-shift but not conversely, is simply that causes explain effects but not conversely, and the reason a conjunction of laws does not explain its conjuncts is that conjunctions do not cause their conjuncts.

In this paper I propose to examine, and in part revive, a time-honoured perspective to inquiry in general and scientific explanation in particular. The perspective is to view inquiry as a search for answers to questions. If there is anything that deserves to be called a working scientist's view of his or her daily work, it surely is that he or she phrases questions and attempts to find satisfactory answers to them.

A few years ago, Bas van Fraassen reminded philosophers of science that there are two central questions that a theory of explanation ought to answer. First, what is a (good) explanation—when has something been explained satisfactorily? Second, why do we value explanations? (van Fraassen, 1977, 1980, ch. 5). For a long time, discussions of explanation concentrated on technical problems connected with the first of these questions, and the second was by and large ignored. But, in fact, I think it is the second question which raises the more fundamental and interesting philosophical issues. I shall offer reasons for thinking that the answer to the first question requires acceptance of the sort of fullblown notion of causation that only a scientific realist can love, and that the answer to the second question requires a realist construal of scientific theories and scientific methodology. My argument will be mainly negative, surveying the problems facing some major alternative accounts of explanation. A full elaboration of the realist perspective will have to await the completion of work in progress.

My title question as it stands is ambiguous, and is in want of some initial clarification. Does the question ask how the explanandum is logically related to the explanans? Or does it ask about the details of the dynamics of the explanation speech-act? Or does it ask how the linguistic ambiguities of explanation questions and answers should properly be unpacked? Or does it ask yet some other question?

The ways of studying explanation, like the ways of understanding the world, are many and varied. By this, I mean more than that the phenomenon of explanation can be studied as it arises in the different disciplines of biology, physics, the social sciences, and the like. Rather, I mean that there are varied disciplines of explanation-study itself. For example, the Hempelian tradition has largely focused on the logic of explanation, and others have focused on the linguistic, psychological, social, and epistemological angles of explanation. Thus, it is not appropriate for me to begin by arguing that explanation is a set of logically related statements or a speech-act (just as one does not begin by arguing ‘the world’ is a sociological or physical phenomenon), but appropriate instead to begin by specifying the explanatory discipline within which I ask my title question.