In this paper, I discuss the key role played by Carl G. Hempel's work on theoretical realism and scientific explanation in effecting a crucial philosophical transition between the beginning and the end of the twentieth century. At the beginning of the century, the dominant view was that science is incapable of furnishing explanations of natural phenomena; at the end, explanation is widely viewed as an important, if not the primary, goal of science. In addition to its intellectual benefits, this transition has important practical consequences with respect to dealing with the global problems humans everywhere will face in the twenty-first century.

This paper discusses several distinct process theories of causality offered in recent years by Phil Dowe and me. It addresses problems concerning the explication of causal process, causal interaction, and causal transmission, whether given in terms of transmission of marks, transmission of invariant or conserved quantities, or mere possession of conserved quantities. Renouncing the mark-transmission and invariant quantity criteria, I accept a conserved quantity theory similar to Dowe's—differing basically with respect to causal transmission. This paper also responds to several fundamental constructive criticisms contained in Christopher Hitchcock's discussion of both the mark-transmission and the conserved quantity theories.

This paper presents a drastically revised version of the theory of causality, based on analyses of causal processes and causal interactions, advocated in Salmon (1984). Relying heavily on modified versions of proposals by P. Dowe, this article answers penetrating objections by Dowe and P. Kitcher to the earlier theory. It shows how the new theory circumvents a host of difficulties that have been raised in the literature. The result is, I hope, a more satisfactory analysis of physical causality.

Can statistical inference shed any worthwhile light on theory change? For many years I have believed that the answer is “Yes.” Let me try to explain why I think so. On my first reading of Thomas S. Kuhn’s The Structure of Scientific Revolutions (1962) I was so deeply shocked at his repudiation of the distinction between the context of discovery and the context of justification that I put the book down without finishing it. By 1969, when a conference was held at the Minnesota Center for Philosophy of Science on the relations between the history of science and the philosophy of science, I had returned to Structure and formed the view that Kuhn’s rejection of this fundamental distinction resulted from his adoption of an inadequate conception of scientific justification. It appeared that he saw scientific confirmation in terms of the traditional hypothetico-deductive (H-D) schema, according to which a scientific hypothesis (or theory) is confirmed by observing the truth of its logical consequences.

When one takes a long look at the concept (or concepts) of scientific explanation, it is possible and plausible to distinguish three fundamental philosophical views. These might be called the epistemic, modal, and ontic. They can be discerned in Aristotle's Posterior Analytics and they are conspicuous in the twentieth-century literature. In its classic form—the inferential version—the epistemic conception takes scientific explanations to be arguments. During the period of almost four decades since the publication of the landmark Hempel-Oppenheim article, “Studies in the Logic of Explanation” (1948), the chairman of this symposium (Carl G. Hempel) has done more than anyone else to articulate, elaborate, and defend this basic conception and the familiar models that give it substance (Hempel 1965), though it has, of course, had many other champions as well. According to the modal conception, scientific explanations do their jobs by showing that what did happen had to happen.

The year 1982 marks the twentieth anniversary of Carl G. Hempel's “Deductive-Nomological vs. Statistical Explanation,” published in Minnesota Studies in the Philosophy of Science, volume III. This work constitutes, to the best of my knowledge, the first extended and systematic philosophical treatment of statistical or probabilistic explanation, and the first serious attempt to articulate explicitly a precise model for such explanations. Because of this fact, it seems to me, we may take 1962 as the year in which the philosophical theory of scientific explanation first entered the twentieth century. By that time, virtually every branch of empirical science made indispensable use of statistical methods and most of them counted statistical generalizations among their important results.

A standard picture of causality has been around at least since the time of Hume. The general idea is that we have two (or more) distinct events which bear some sort of cause-effect relation to one another. There has, of course, been considerable controversy regarding the nature of both the relation and the relata. It has sometimes been maintained, for instance, that facts or propositions (rather than events) are the sorts of entities which can constitute the relata. It has long been disputed whether individual events or only classes of events can sustain cause-effect relations. The relation itself has sometimes been taken to be that of sufficient condition, sometimes necessary condition, or perhaps a combination of the two. Some authors have even proposed that certain sorts of statistical relations constitute causal relations.

Carl G. Hempel has often stated that inductive-statistical explanations, as he conceives them, are inductive arguments. This discussion note raises the question of whether such arguments are to be understood as (1) arguments of the traditional sort, containing premises and conclusions, governed by some sort of inductive “acceptance rules,” or (2) something more closely akin to Carnap's degree of confirmation statements which occur in an inductive logic which entirely eschews inductive “acceptance rules.” Hempel's writings do not seem unequivocal on this issue. It is suggested that adoption of construal (2) would remove the need for Hempel's high probability requirement on I-S explanations.

Carl G. Hempel's doctrine of essential epistemic relativization of inductive-statistical explanation seems to entail the unintelligibility of the notion of objective homogeneity of reference classes. This discussion note explores the question of whether, as a consequence, essential epistemic relativization also entails the unintelligibility of the doctrine of indeterminism.

The propagation of causal influences through space-time seems to play a fundamental role in scientific explanation. Taking as a point of departure a basic distinction between causal interactions (which are localized in space-time) and causal processes (which may extend through vast regions of space-time), this paper attempts an analysis of the concept of causal propagation on the basis of the ability of causal processes to transmit “marks.” The analysis rests upon the “at-at” theory of motion which has figured prominently in the resolution of Zeno's arrow paradox. It is argued that this explication does justice to the concept of the ability of causal processes to transmit causal influence without invoking anti-Humean “powers” or “necessary connections.”

Since Professor Greeno's paper is, to my mind, both philosophically interesting and somewhat technical, it seems to me that the most useful function I can serve as a commentator is to try to provide some of the background necessary to understand the paper, and to attempt to put his discussion in some philosophical perspective. My main aim will be to relate his discussion to the issues that have been at the forefront of the philosophical discussion of scientific explanation in recent years.

It would be hard to dispute the claim that Professor Carl HempePs work has dominated the discussion of the nature of scientific explanation for the last twenty-two years - since the publication of the classic article with Paul Oppenheim on the logic of explanation.

After describing a new method of synchronizing spatially separated clocks by means of clock transport, this paper discusses the philosophical import of the existence of such methods, including those of Ellis and Bowman and of Bridgman, with special reference to the Ellis-Bowman claim that “the thesis of the coventionality of distant simultaneity ... is thus either trivialized or refuted.” I argue that the physical facts do not support this philosophical conclusion, and that a substantial part of their argument against Reichenbach, in particular, is misdirected. Finally, I suggest that Ellis and Bowman employ seriously unclear notions of triviality and “good physical reasons” that tend to obscure rather than clarify the basic philosophical issues. An objective criterion of nontriviality of conventions is advanced.

This rejoinder will be divided into two parts. The first part will be devoted to what appear to be serious disagreements between Professor Kyburg and me. I shall try to show that these disagreements are far more apparent than real. The second part will contain my criticism of Kyburg's constructive suggestion on the nature of explanation.

A consideration of some basic problems that arise in the attempt to provide an adequate characterization of statistical explanation is taken to show that an understanding of the nature of scientific explanation requires us to deal with the philosophical problems connected with the nature of prior probabilities.