Introduction (Full1 Text)
- The opposition between empiricism and realism is old, and can be introduced by illustrations from many episodes in the history of philosophy. The most graphic of these is perhaps provided by the sense of philosophical superiority the participants in the early development of modern science felt toward the Aristotelian tradition. In that tradition, the realists held that regularities in the natural phenomena must have a reason (cause, explanation), and they sought this reason in the causal properties, constituting what they called the substantial forms or natures, of the substances involved in natural processes. The nominalists, who denied the reality of these properties, were in the position of having to reject such requests for explanation.
- The philosophers engaged in developing the philosophical foundations of modern science had apparently escaped this dilemma. Without postulating such causal properties, forms, or ‘occult qualities', they could still explain the regularities that are observed in nature. To give an account of such phenomena as heat or chemical reactions in terms only of mechanical attributes, they realized quite well, required at least an atomic theory of matter. But I suppose it is clear that they will face that same dilemma again for the regularities they postulate in the behaviour of the atomic parts. No mechanical explanations are possible there, since the atoms have no further parts. So either they must attribute specific powers, qualities, and causal properties to those atoms to explain why they act and react in the way they actually do; or else they must, like the nominalists before them, reject the request for explanation.
- In addition, they have gained a problem. Part of the motivation for the nominalist rejection of the Aristotelian realists' world of powers, properties, dispositions (made famous by Moliere's virtus dormitiva) was epistemological. The observation of the phenomena did not point unambiguously to the supposed causal connections behind them. This problem exists similarly for the atomic hypotheses: the phenomena do not decide their truth or falsity, though they are perhaps better explained by one hypothesis than by another. Subsequent scientists intent on clarifying the philosophical basis of their discipline found it ever more difficult to reconcile their professed empiricism and antipathy to metaphysics with an unqualified belief in hypotheses that describe a supposed world behind the phenomena.
- This led in the nineteenth century to the phenomenalism of Ernst Mach, the conventionalism of Henri Poincare, and the fictionalism2 of Pierre Duhem. In the twentieth, the logical empiricism of Hans Reichenbach and logical positivism of Rudolph Carnap were further developments in this radical turn to empiricism.
- Today, however, no one can adhere to any of these philosophical positions to any large extent. Logical positivism, especially, even if one is quite charitable about what counts as a development rather than a change of position, had a rather spectacular crash. So let us forget these labels which never do more than impose a momentary order on the shifting sands of philosophical fortune, and let us see what problems are faced by an aspirant empiricist today. What sort of philosophical account is possible of the aim and structure of science?
- Studies in philosophy of science divide roughly into two sorts. The first, which may be called foundational, concerns the content and structure of theories. The other sort of study deals with the relations of a theory on the one hand, to the world and to the theory-user on the other.
- There are deep-going philosophical disagreements about the general structure of scientific theories, and the general characterization of their content. A current view, not altogether uncontroversial but still generally accepted, is that theories account for the phenomena (which means, the observable processes and structures) by postulating other processes and structures not directly accessible to observation; and that a system of any sort is described by a theory in terms of its possible states. This is a view about the structure of theories shared by many philosophers who nevertheless disagree on the issues concerning a theory's relation to the world and to its users. Opponents of that view will at least say, I think, that this account of what science is like is true ‘on the face of it', or correct as a first approximation.
- One relation a theory may have to the world is that of being true, of giving a true account of the facts. It may at first seem trivial to assert that science aims to find true theories. But coupled with the preceding view of what theories are like, the triviality disappears. Together they imply that science aims to find a true description of unobservable processes that explain the observable ones, and also of what are possible states of affairs, not just of what is actual. Empiricism has always been a main philosophical guide in the study of nature. But empiricism requires theories only to give a true account of what is observable, counting further postulated structure as a means to that end. In addition empiricists have always eschewed the reification of possibility (or its dual, necessity). Possibility and necessity they relegate to relations among ideas, or among words, as devices to facilitate the description of what is actual. So from an empiricist point of view, to serve the aims of science, the postulates need not be true, except in what they say about what is actual and empirically attestable.
- When this empiricist point of view was represented by logical positivism, it had added to it a theory of meaning and language, and generally a linguistic orientation. Today that form of empiricism is opposed by scientific realism, which rejects not only the views on meaning of the positivists, but also those empiricist tenets which I outlined in the preceding paragraph. My own view is that empiricism is correct, but could not live in the linguistic form the positivists gave it. They were right to think in some cases that various philosophical perplexities, misconceived as problems in ontology and epistemology, were really at bottom problems about language. This opinion is correct especially, I think, about problems concerning possibility and necessity. The language of science, being a proper part of natural language, is clearly part of the subject of general philosophy of logic and language. But this only means that certain problems can be set aside when we are doing philosophy of science, and emphatically does not mean that philosophical concepts must be one and all linguistically explicated. The logical positivists, and their heirs, went much too far in this attempt to turn philosophical problems into problems about language. In some cases their linguistic orientation had disastrous effects in philosophy of science. Scientific realism, however, pursues the antithetical error of reifying whatever cannot be defined away.
- Correlative to discussions of the relation between a theory and the world, is the question what it is to accept a scientific theory. This question has an epistemic dimension (how much belief is involved in theory acceptance?) and also a pragmatic one (what else is involved besides belief?). On the view I shall develop, the belief involved in accepting a scientific theory is only that it ‘saves the phenomena', that is, correctly describes what is observable. But acceptance is not merely belief. We never have the option of accepting an all-encompassing theory, complete in every detail. So to accept one theory rather than another one involves also a commitment to a research programme, to continuing the dialogue with nature in the framework of one conceptual scheme rather than another. Even if two theories are empirically equivalent, and acceptance of a theory involves as belief only that it is empirically adequate, it may still make a great difference which one is accepted. The difference is pragmatic, and I shall argue that pragmatic virtues do not give us any reason over and above the evidence of the empirical data, for thinking that a theory is true.
- So I shall argue for an empiricist position, and against scientific realism. In some ways, philosophy is a subject of fashions — not more so than other intellectual disciplines, I suppose, but at least to the extent that almost any philosopher will begin by explaining that he opposes the ‘dominant' or ‘received' view, and present his own as revolutionary. It would be quite suspicious therefore if I were to say at this point that scientific realism has become dominant in philosophy of science. Others have certainly characterized it as the emerging victor: Isaac Levi recently wrote, ‘My own view is that the coffin of empiricism is already sealed tight.' There is therefore at least already considerable sentiment on the side of realists that they have replaced the ametaphysical empiricism of the positivists. The empiricist position I mean to advocate will be strongly dissociated from both. (See Chapter 2 §1.2 and Chapter 1 for some remarks on positivism.)
- In part my argument will be destructive, countering the arguments brought forward by scientific realists against the empiricist point of view. I shall give a momentary name, ‘constructive empiricism', to the specific philosophical position I shall advocate. The main part of that advocacy will be the development of a constructive alternative to scientific realism, on the main issues that divide us: the relation of theory to world, the analysis of scientific explanation, and the meaning of probability statements when they are part of a physical theory. I use the adjective 'constructive' to indicate my view that scientific activity is one of construction rather than discovery: construction of models that must be adequate to the phenomena, and not discovery of truth concerning the unobservable. The baptism of this philosophical position as a specific ‘ism' is not meant to imply the desire for a school of thought; only to reflect that scientific realists have appropriated a most persuasive name for themselves (aren't we all scientific, and realists, nowadays?), and that there is after all something in a name.
Footnote 1: Longer quotations excised.
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