The Realism/Antirealism Debate in the Philosophy of Science

Transcription

1 The Realism/Antirealism Debate in the Philosophy of Science Dissertation zur Erlangung des akademischen Grades des Doktors der Philosophie (Dr. phil.) an der Universität Konstanz, Geisteswissenschaftliche Sektion, Fachbereich Philosophie vorgelegt von Radu Dudau Konstanz, Mai 2002

2 Contents 1 Introduction What is realism? Varieties of scientific realism The Success Arguments for Scientific Realism The No Miracle Argument Smart s no cosmic coincidence argument and Maxwell s argument from the epistemic virtues of theories The argument from realism s exclusive capacity to give causal explanations Van Fraassen s arguments against IBE The context-dependency objection The inconsistency objection Arguments against the ability of IBE to link empirical success with truthlikeness The downward path The upward path The Success of Methodology Argument Fine against IBE The Experimental Argument for Entity Realism Atoms from fictions to entities The common cause principle Manipulability, entities, and structure Entity realism and theory realism On structural realism The Underdetermination Argument: The Theoretical/Observational Distinction The theoretician s dilemma

3 4.2 Van Fraassen s observable/unobservable distinction Maxwell s continuity argument The technological argument The phenomenology of science The incoherence arguments Fodor s theory/observation distinction Against Meaning Holism Psychological arguments Kukla s observable/unobservable distinction Against the Underdetermination Thesis Against algorithmically generated empirical equivalents The dismissal of T The dismissal of T The insufficiency of Kukla s solution to the problem of scientific disregard Versions of empirical equivalence Arguments against the entailment thesis EE does not entail UD Social Constructivism Varieties of social constructivism The reflexivity problem The reflexivity of metaphysical constructivism The reflexivity of epistemic constructivism The reflexivity of semantic constructivism Spatial and temporal inconsistencies Spatial inconsistencies Temporal inconsistencies A Case for Selective Scientific Realism: S-Matrix Theory The S-Matrix Theory (SMT): a historical case study Quantum field theory (QFT) The origins of the S-matrix. S-matrix theory (SMT) Philosophical conclusions Appendix: Truthlikeness 162 A.1 Popper s theory of verisimilitude A.2 The possible worlds/similarity approach

4 A.3 Anti-truthlikeness: Giere s constructive-realist proposal Summary 175 Zusammenfassung 178 References 181 4

5 Chapter 1 Introduction 1.1 What is realism? The term realism designates a class of philosophical doctrines about reality. What these doctrines have in common is the claim that we confront a material world, existing objectively and independently of our thought and experience. Typically, this ontological claim is accompanied by the epistemic claim that we can and indeed do have knowledge of the external world. Upon careful inspection, the ontological thesis reveals two dimensions of realism: an independence dimension, and an existence dimension. An entity exists independently in that it does not depend on our epistemic capacities. In other words, it is not constituted by our knowledge, by the synthesizing powers of our mind, nor by our imposition of concepts or theories. (Devitt 1984: 13). In this sense, Kant s phenomenal world and Goodman s worldversion (see 6.3) do not have independent existence. Realism allows for a part of the world to be dependent on our epistemic capacities. As will be shown in chapter 6, we can accept that many facts about the world are social constructions. However, it is presupposed that there is a brute external world out of which these facts are constructed. The view that all the facts about the world are constructed represents a radical kind of constructivism (see 6.1) which splits with realist assumption of an external material world. A corollary of this assumption is that the world does not entirely consist of mental states. The realist s antagonist in this dimension is the idealist. The idealist argues that the mind (or spirit) constitutes a fundamental reality and that the physical world exists only as an appearance to or as an expression of the mind. The radical constructivist is an idealist, one who, following Berkeley, thinks of physical objects as collections of sensory ideas. The existence dimension of realism is concerned with the entities that are 5

6 claimed to exist. We can picture the existence dimension as a vertical one, having at its lowest level the claim that something exists objectively and independently of the mental (Devitt 1984: 15). Devitt labels it a fig-leaf realism, committed to nothing above an undifferentiated and uncategorized brute world. This might be Goodman s (1978) world without kinds or order or motion or rest or pattern, a world not worth fighting for (1978: 20). (We shall see in chapter 6, when discussing the spatial and temporal inconsistencies of constructive empiricism, that this world is not as worthless as some seem to believe.) Next on the vertical dimension comes the claim that common-sense entities, such as stones and trees, exist independently of us, thus representing a commonsense realism. A significant move upwards on the vertical dimension consists in the claim that the unobservable entities posited by scientific theories, such as electrons and genes, exist independently of us. This describes scientific realism, the doctrine we are mostly concerned with here. Finally, to maintain that abstract entities that will be labelled in section 6.1 ideas such as numbers, values, propositions, etc., exist, is to adopt abstract realism. As Kukla (1998: 4) remarks, in spite of the logical independency of these sorts of realism, there is a tendency of those who adopt any of these levels to accept all the lower levels. Scientific realists are most of the times commonsense realists, as abstract realists have no problems in admitting both the existence of stones and of electrons. However, there are notable exceptions. Platonism is a species of abstract realism which admits exclusively the existence of abstract entities. The above mentioned epistemic claim presupposes, as Wright (1993) puts it, two sorts of ability: the ability to form the right concepts for the classification of genuine, objective features of the world; and the ability to come to know, or at least reasonably to believe, true statements about the world whose expression those concepts make possible. (Wright 1993: 2) The epistemic opponent of the realist is the sceptic. The sceptic does not dispute the independent existence of an external world, but refuses to admit that our epistemic practices can provide us with knowledge or warranted belief about this world. Wright s above passage also introduces a semantic aspect in the discussion of realism: the truth of the statements about the world. The semantic issue of realism is whether truth is an objective relation between language and reality. It is common to take semantic realism as defining truth as a correspondence 6

7 between language and reality. However, one ought to note the diversity of views about truth within the realist camp. Most of the scientific realists embrace indeed a correspondence theory of truth. Among them, some take truth as constitutive of realism: Hooker (1974: 409) states that realism is a semantic thesis, the view that if a scientific theory is in fact true then there are in the world exactly those entities which the theory says there are.... ; Ellis defines scientific realism as the view that the theoretical statements of science are, or purport to be, true generalized descriptions of reality (1979: 28); according to Hesse (1967), realism holds that theories consist of true or false statements referring to real or existing entities. (1967: 407). Other supporters of the correspondence theory of truth believe that scientific realism has nothing essential to do with truth (e.g. Devitt 1984; 2001). Nonetheless, other realists believe that truth has no nature at all, hence no bearing to scientific realism. The deflationary views Ramsey s (1927) redundancy theory, Quine s (1970) disquotationalism, Horwich s (2001) minimalism share the conviction that there is nothing more to the truth of a sentence/proposition than our commitment to the sentence/proposition itself. It is also interesting how most antirealists find it convenient to construe scientific realism in terms of the correspondence theory of truth. Van Fraassen, for example, ascribes scientific realism the claim that science aims to give us, in its theories, a literally true story of what the world is like (1980: 8). After having described the issues of the ontological, the epistemic, and the semantic aspects of realism, it is important that we keep them distinct. Provided that one believes in ontological realism, it is optional for one to be an epistemic, and/or a semantic realist. For one thing, one may subscribe to ontological realism without epistemically doing so: belief in the existence of an external world does not entail that this world is in any sense ascertainable to us. The reverse does not hold: one cannot have knowledge about the world if there is no world. It follows that epistemic realism logically entails ontological realism. For another, one can be a semantic realist without thereby being an epistemic realist: one can maintain that statements about the world have truth-values, regardless of whether we can come to know them or not. At the same time, epistemic realism cannot be in place without semantic realism. One cannot have knowledge about anything in the world unless statements about the world are truth-valuable. It follows that epistemic realism logically entails semantic realism. The conceptual relation between ontological and semantic realism seems to be one of independence. On the one hand, one can admit the independent existence of a physical world without for one s beliefs to refer to anything in the world. Thus, ontological realism does not entail semantic realism. On the other hand, semantic realism specifies how the world should be like in order to 7

8 make sentences about the world truth-valuable (i.e. either true or false). This in no way involves commitment to the view that the world is indeed like this. Thus, semantic realism does not entail ontological realism. Certainly, these conceptual relationships should not hinder our awareness of the intertwining of ontological, semantic, and epistemic issues in a constitutive sense: the ontological thesis has been formulated in terms of external world s independence of our epistemic capacities. Besides, both the ontological and the epistemic thesis ought may need to be subjected to a meaning analysis. 1.2 Varieties of scientific realism Scientific realism has been located on the vertical, ontological dimension of realism. It has been defined via the claim that the unobservable entities posited by scientific theories, such as electrons and genes, exist independently of us. We can acquire a more precise understanding of scientific realism by analyzing it under the ontological, semantic, and epistemic aspects that we have identified within the general doctrine of realism. Metaphysical scientific realism henceforth MSR is the claim that the unobservable entities posited by science exist objectively and independently of us. It assumes the existence of common-sense entities like stones and trees. We saw that the opponent of the doctrine of realism on the ontological line was the idealist. However, to deny scientific realism does not in the least involve a radical departure from belief in the existence of an independent external world. One can dismiss scientific realism while embracing commonsense realism. From the position of commonsense realism, a rejection of MSR will mean either to take all sentences about scientific unobservables as being false; or to be agnostic about the existence of such entities; or, finally, to take it that all such sentences are ill-formed, hence nonsensical. Semantic scientific realism henceforth SSR is the claim that all statements about theoretical entities have truth values. As pointed out above, semantic realism only tells us what the truth-makers of factual sentences are, i.e. how the world should be in order to make these sentences truth-valuable. This does not involve that the world is indeed like that. Particularized to SSR, the claim is that statements about theoretical entities are truth-valuable. As Kukla indicates, the statement Electrons are flowing from point A to point B would be true if and only if electrons were indeed flowing from A to B. (Kukla 1998: 8). Yet to accept all of this does not mean that the actual existence of electrons must be accepted, nor anything else about their properties. The rejection of SSR can well take place from the position of commonsense semantic realism. This is the stance taken in semantic instrumentalism, 8

9 through both its variants: eliminative and non-eliminative. Eliminative semantic instrumentalism (also known as reductionism) states that theoretical terms are to be defined in observational terms, and that theoretical statements are to be translated into observational statements. Presupposed, of course, is a clear-cut distinction between the theoretical and the observational, an idea which we shall criticize and reject in chapter 4. Non-eliminative semantic instrumentalism views theoretical terms as semantically uninterpreted instruments useful for organizing observations. Epistemic scientific realism henceforth ESR is usually taken to be the claim that we can and do acquire knowledge about the existence of theoretical entities. ESR requires multiple qualifications. (1) According to the object of knowledge, there are two kinds of ESR: a restrained kind, claiming knowledge only of the existence of theoretical entities, and an extended one, additionally claiming knowledge of the properties of, and relations between, these entities. The former will concern us throughout this work. (2) According to the strength of the knowledge claims, there is a strong ESR stating that we know our scientific theories to be strictly true. Yet such an infallibilism is so fragile as to be untenable. First, all past scientific theories turned out to be stricto sensu false, so that, by pessimistic meta-induction, we can conclude to the very low probability of our current theories being all true. Second, any scientific theory involves idealizations, approximations, and ceteris paribus clauses, which inevitably induce a degree of imprecision in the scientific statements. Therefore, to embrace epistemic standards so high so as to accept only literally true sentences would mean virtually to expel the entire body of science (see the Appendix). Scientific realists have learned the lesson of fallibilism. They do not actually claim more than knowledge of the approximate truth of our well-established theories. Approximate truth has been criticized for lack of conceptual clarity by both friends and foes. As shown in the Appendix, while some scientific realists, such as Devitt (1991) and Psillos (1999) advocate for an intuitive notion of approximate truth, critics among which Laudan (1981) is the most adamant object that the concept lacks the minimal clarity needed in order to ensure whether it can be of any philosophical avail. However, Niiniluoto (1999) offers a robust theory of approximate truth and of its cognates, truthlikeness and verisimilitude. We rely upon it when embracing the claim that we have knowledge of the approximate truth of our best theories. A weaker epistemic claim is that we are rationally warranted to believe in our well-established theories. This position circumvents the attack by pessimistic meta-induction, but only at the price of a major inconvenience: it 9

10 cannot explain the methodological success of science (see 2.4). By descending even further down the epistemic scale, we reach the point where is it claimed that it is logically and nomologically possible to attain a state that warrants belief in a theory. (Kukla 1998: 11). Such a view can barely explain anything about science. I take it that its only merit is didactic: it shows how closely one can get to scepticism while still remaining an epistemic realist. Anything that goes underneath this level ought to be called epistemic antirealism. Van Fraassen s constructive empiricism, which we shall discuss in detail, is a famous species of epistemic antirealism. Van Fraassen believes in the truth of scientific theories with respect to their observable posits, but declines belief when it comes to unobservables. Constructive empiricism takes empirical adequacy, and not truth, as the goal of science. Accordingly, empirically successful theories are to be accepted, i.e. believed to be empirically adequate, and not believed to be (approximately) true. We shall devote extensive space to criticizing constructive empiricism in several respects see sections 2.1, 2.4, and 3.2. After having exposed the varieties of scientific realism and the conceptual relations between them, it is appropriate to present our working definition of scientific realism: Scientific realism is the doctrine according to which (i) Most of the essential unobservables posited by our well-established current scientific theories exist independently of our minds. (ii) We know our well-established scientific theories to be approximately true. Claim (i) was stated by Devitt (2003) and presents the ontological aspect of scientific realism. We shall discuss in chapter 6 one important contender of the independence dimension of realism: social constructivism. It will be distinguished between many varieties of social constructivism, which will be inspected from the standpoint of their consistency. Among them, radical social constructivism denies that there is any part of the external world which is not of our making; all facts are the outcomes of collective intentional activity. Thus, radical constructivism turns out to be a form of idealism. Claim (ii) underscores the epistemic aspect of our concept of scientific realism. Epistemic scientific realism is seriously challenged by the underdetermination argument, which constitutes the themes of chapters 4 and 5. One premise of the underdetermination argument is the empiricist assumption that the only warranted knowledge is that concerning observable entities. The second premise is that for any given body of observational evidence, there are indefinitely many theories which entail it. Therefore, as the argument goes, 10

11 the epistemic ascent to any particular theory is blocked. In other words, theories are underdetermined by the empirical data. In chapter 4, we shall criticize and dismiss the underdetermination argument by showing that there is no principled way to draw a distinction between the observable and the theoretical, on which its first premise relies. We argue next (chapter 5), that even if such a distinction could be made, the second premise (the empirical equivalence thesis) cannot be established in a form that generally blocks epistemic ascent to the best theory. An implicit point about the definition of scientific realism concerns its scope of application. Scientific realism is often taken as a global, overarching doctrine, appropriate in accounting for most cases of successful scientific practice. However, scientific realism ought to be more true to scientific life: it ought to do justice to the cases in which, indeed, scientific theories have merely an instrumental value, and incorporate elements constructed without causal constraints. Chapter 7 illustrates such a case (the S-matrix theory of strong interaction) and pleads for a selective scientific realism. 11

12 Acknowledgments I am very much obliged to my doctoral supervisor, Professor Wolfgang Spohn, for his invaluable assistance. His criticism and demand for clarity and precision was doubly outweighed by his patience and confidence in the merits of my work. My gratitude is also extended to professors William Newton-Smith, James Robert Brown, Michael Devitt, and Gereon Wolters for their advice and guidance through the intricate paths of scientific realism. Ludwig Fahrbach and Erik Olsson provided me with welcome criticism and commentary, either by reading various sections of my dissertation, or through conversation about its contents. This dissertation would not have reached completion, were it not for the financial support of the Open Society Institute and the Herbert Quandt Stiftung. I am thankful to Dr. Gerhild Framhein for her generosity and understanding, as well as to Professor Andrei Hoisie. I am in debt to the DAAD for making possible my academic contact with Konstanz University. I am also very much indebted to Professors Erhard Roy Wiehn and Kathleen Wilkes for their moral support. Finally, I wish to thank my friends Debbie Allen for improving the English standards of the present work, and Sascha Wolff for his patient LaTex advising. Special thanks to my friend Till Lorenzen for all his support. 12

13 Chapter 2 The Success Arguments for Scientific Realism It is virtually incontestable that science is an immensely successful enterprise. First, science is successful in entailing successful predictions. Second, scientific methods have proven to be effective in generating successful theories. Let us call the former aspect the empirical success of science, and the latter, the methodological success of science. According to the scientific realist, both sorts of success are non-trivial facts. They demand explanation: Why do scientific theories tend to produce correct observational predictions and to deliver adequate explanations of observable phenomena? By which means is scientific methodology so good at forming successful belief systems? The reason why the scientific realist thinks that the success of science undergirds his doctrine is that he arguably has the best explanations for both the empirical and the methodological success of science. Indeed, his argumentation relies on an inference to the best explanation (henceforth IBE): the best explanation for the fact that scientific theories are empirically successful is that theoretical terms typically refer, and that theoretical statements are approximately true or truthlike. Similarly, the best explanation for the methodological success of science is that scientific methodology is reliable (in a sense to be explained in subsection 2.4.2). It is important to emphasize that the explananda of the two IBEs are different. On the one hand, the empirical success argument seeks to explain the success of theories in systematizing and explaining phenomena, and in making highly confirmed predictions. On the other, the methodological success argument attempts to explain the success of scientific methods in producing successful theories. 1 1 As we shall see in section 2.2, one antirealist argument capitalizes on the alleged insufficient stringency of IBE at the methodological level. 13

14 Second, the explanandum of the empirical success comprises two parts, asserting, respectively, that (i) theoretical terms are referential, and (ii) theoretical statements are approximately true. I would like offer two remarks about them. The first and general one is that, in line with Devitt (1984; 2003), I take it that it is not essential to state the argument by means of the terms refer and true :...such usage should be seen as exploiting the disquotational properties of the terms with no commitment to a robust relation between language and the world. The realist argument should be that success is explained by the properties of unobservables, not by the properties of truth and reference. So the argument could be urged by a deflationist. (Devitt 2003: Fn. 11). I shall not go into the details of any specific theory of truth, since I take it that no particular view of truth is constitutive of realism see section 1 in the introductory chapter. I subscribe to Devitt s (1984: 4) Third Maxim that requires us to settle the realism issue before any semantic issue. The benefits of disquotation also extend to the concepts of approximate truth and truthlikeness. Instead of talking about the approximate truth of the sentence a is F, we can just talk of a s approximately being F. However, with respect to approximate truth and truthlikeness, I often prefer to talk in these terms instead of disquotation. The reason lies in the fact that, on many occasions, we want quantitative comparisons of truthlikeness, and that, as such, disquotation would only make them more awkward. Besides, I also believe that we have a robust and serviceable account of truthlikeness given by Niiniluoto (1999) (see A.2). My other remark about the distinction between the two parts within the explanandum of the empirical success of science is that each of them corresponds to a different version of realism. The claim that most (essential) unobservable entities posited by scientific theories exist independently of our minds, language, and representations defines the doctrine of scientific entity realism. While entity realism is committed to science s being mostly right about the entities it posits, it is partly noncommittal on the truth values of those theoretical sentences describing the properties of entities and the relations between them. Nonetheless, many realists defend a logically stronger version of scientific realism, committed not only to theoretical entities, but also to the descriptions of their properties. This is the doctrine that Devitt calls strong scientific realism: most of the essential unobservables of well-established current scientific theories exist mind-independently and mostly have the properties attributed to them by science. (Devitt 2003). Since strong scientific realism seems to be 14

15 embraced by most self-declared scientific realists, I label it scientific realism and distinguish it from mere entity realism. It is clear that scientific realism implies entity realism, but not the converse. Moreover, the best-known advocates of the latter (Hacking 1983; Cartwright 1983) explicitly argue against what they call theory realism realism about scientific laws thereby denying the scientific realist claim complementary to entity realism. As we have seen, the argumentation for scientific realism proceeds by IBE. This implies that any IBE in favor of scientific realism will also support entity realism. Yet, entity realism enjoys supplementary support from the so-called experimental argument, which will be the subject of the next chapter. The efficiency of IBE in defending scientific realism has been detracted in two important ways: first, some anti-realists (van Fraassen (1984; 1989); Fine (1984; 1986; 1991)) levelled objections of principle against IBE-based arguments, denouncing them for being context-dependent, inconsistent, and viciously circular. I dismiss these objections in 2.2 and 2.4. A different kind of criticism concerns IBE s specific role in the defence of scientific realism. Laudan (1984) deployed the most extensive attack of this kind. I argue against it in section 2.3. Let us now outline the argumentative strategy of this chapter. Section 2.1 presents several explanationist arguments for the empirical success of science: Putnam s (1975; 1978) no miracle argument (NMA), which is the most popular formulation of an IBE-based explanation of the success of science; Smart s (1963) no cosmic coincidence argument, and Maxwell s (1970) argument from the empirical virtues of realistically interpreted theories; and finally, my argument based on the exclusive ability of realistically interpreted theories to give causal explanations. Section 2.2 investigates the general objections against IBE, while 2.3 continues with a detailed discussion of the alleged inability of IBE to connect the empirical success of science with the approximate truth of theories. Section 2.4 discusses Boyd s (1984; 1985) explanation of the methodological success of science, as well as Fine s replies to it. 2.1 The No Miracle Argument The most famous argument from the empirical success of science is Putnam s (1975) no miracle argument (henceforth NMA). NMA claims that the predictive success of scientific theories is best explained by their being approximately true: The positive argument for realism is that it is the only philosophy of science that does not make the success of science a miracle. That terms in mature scientific theories typically refer (this formulation is due to 15

16 Richard Boyd), that the theories accepted in a mature science are typically approximately true, that the same terms can refer to the same even when they occur in different theories these statements are viewed not as necessary truths but as parts of the only scientific explanation of the success of science, and hence as part of any adequate description of science and its relations to its objects. (Putnam 1975: 73) The argument emphasizes the overwhelming improbability (indeed the miracle) of any explanation which would not rely on the referentiality of theoretical terms and on the approximate truth of scientific theories. Putnam does not bother here to distinguish between entity realism and scientific realism. However, if cogent, his argument will defend both the claim that theoretical terms typically refer, and the logically stronger one that the theories themselves are approximately true. NMA is obviously an IBE-based argument: to accept that theoretical terms refer, and that scientific theories are approximately true is the best explanation of why phenomena are the way they are predicted by those theories. This, according to NMA, is not only a good explanation of empirical success, but also the best explanation we have for it. Suppose we ask, for example, why are observations that scientists report on as if there were atoms? The realist answer is: because there are atoms and stronger claim because the atomic theories are approximately true. Were this not the case, what else but a miracle would explain the empirical success of theories? (See section 3.1 for a historical case study of modern atomism). As it can be seen, the explanans of NMA is not the strict truth of scientific theories, but their approximate truth, or truthlikeness. Strict truth deductively entails the truth of all consequences of a given theory. However, theoretical descriptions are most of the time only approximately correct or truthlike. Approximate truth and truthlikeness are not uncontroversial notions. Among others, Laudan (1981) maintains that these are undefined notions, and accordingly disapproves the realist s explanatory appeal to such mumbo-jumbo (1981: 32). However, for one thing, the notion of approximate truth has a quite strong intuitive support. As Devitt (2003) notes, science and life are replete with such explanations; for example, a s being approximately spherical explains why it rolls. For another, it is surely not the case that approximate truth is an undefined notion. Quite the contrary, there is an appreciable literature approaching a quantitative definition of approximate truth via its related concept, truthlikeness see, among others, Oddie (1986), Kuipers (1992), and Niiniluoto (1987; 1999). As far as I am concerned, I favor Niiniluoto s similarity approach (see the Appendix). I take it to be a robust account of truthlikeness, dependable for most purposes of our analysis. 16

17 2.2 Smart s no cosmic coincidence argument and Maxwell s argument from the epistemic virtues of theories NMA has been preceded by quite similar statements by J. J. C. Smart (1963) and Grover Maxwell (1970). In Smart and Maxwell s approaches, the archrival of realism is the instrumentalist understanding of science. Semantic instrumentalism assumes that the language of science is to be divided into an observational and a theoretical part. The observational language contains, apart from the logical vocabulary, only observational terms, directly connected to the empirical world through operational definitions. As pointed out in the introductory chapter, non-eliminative semantic instrumentalism takes theoretical terms to have the role of systematizing observational statements, thus making theories more simple and economical. They are linguistic instruments which have no referents, so that the statements containing them do not have truth values. Thus, according to instrumentalism, statements about, say, electrons are nothing but instruments meant to enable us to make predictions at observational level of tracks in the cloud chamber. 2 For reasons of convenience, instrumentalism is sometimes depicted in terms of a black box metaphor. In the suitable description by Bird, One puts into the box information regarding observed background conditions, and the box generates predictions regarding what one will observe. What one wants from such a black box is that if the input information is accurate, then the predictions it yields will be accurate too. We are not especially concerned with the mechanism inside the box. That can be anything so long as it works. In particular, there is no requirement that it depict the way the world is. (Bird 1999: 125 6) Smart argued that instrumentalism has no means to account for a multitude of ontologically disconnected phenomena other than belief in cosmic coincidences. By contrast, scientific realism offers a close-at-hand and reasonable explanation, which leaves no room for large scale fortuitousness. As Smart puts it, Is it not odd that the phenomena of the world should be such as to make a purely instrumental theory true? On the other hand, if we interpret a theory in the realist way, then we have no need for such a cosmic coincidence: it is not surprising that galvanometers and cloud chambers behave in the sort of way they do, for if there are really electrons, etc., this is just what we should expect. (Smart 1963: 39) 2 I shall henceforth be explicit about the varieties of instrumentalism whenever the distinction is relevant, and the context itself cannot indicate it. 17

18 At a first sight, Putnam s and Smart s formulations are virtually identical: the first speaks of miracles, while the latter speaks of cosmic coincidences. However, as Psillos (1999: 72 3) has pointed out, their argumentative structures are different. While Putnam s argument is empirical, Smart s one is a conceptual analysis; i.e., while Putnam s NMA relies on an abductive inference, Smart s argument is part of his attempt to clarify a conceptual dispute concerning the ontological foundations of science. The realist instrumentalist dispute instantiates such conceptual confrontation with respect to the interpretation of scientific theories. As Psillos properly states,...smart s no cosmic coincidence argument relies on primarily intuitive judgements as to what is plausible and what requires explanation. It claims that it is intuitively more plausible to accept realism over instrumentalism because realism leaves less things unexplained and coincidental than does instrumentalism. Its argumentative force, if any, is that anyone with an open mind and good sense could and would find the conclusion of the argument intuitively plausible, persuasive and rational to accept though not logically compelling. (Psillos 1999: 73) So Smart argued from the intuitive plausibility of the realist position. His no cosmic coincidence argument relies on intuitive judgements about what is plausible and what needs to be explained. The point, as Psillos phrases it, is that it s intuitively more plausible to accept realism over instrumentalism because realism leaves less things unexplained and coincidental than realism does (cf. Psillos 1999: 73). 3 An attempt to account for the plausibility of the realist judgements was made by Maxwell (1970), who turned to the epistemic virtues such as explanatory power, simplicity, comprehensiveness, lack of ad hocness of realistically interpreted scientific theories: As our theoretical knowledge increases in scope and power, the competitors of realism become more and more convoluted and ad hoc and explain 3 We should note that many realists are wary of talk of conceptual analysis and a priori reasoning. The so-called epistemological naturalists (see BonJour (1998) defend the thesis that the one and only way for knowledge acquisition is empirical. Devitt s (1997, 1998) motivation for this position is, first, that the very idea of the a priori is obscure and second, that it is unnecessary, since an empirical approach of justification seems to be available. Stich (1998) argues that all that can be obtained by analysis knowledge about our implicit assumptions about the nature of things assumptions embedded in our language and no knowledge about the nature of things themselves. However, without trying to resolve here this complex debate, I agree with Jackson s (1998) that there is a lot of closet conceptual analysis going on (1998: vii). For example, one s utterance that sentence Jones is six foot and Smith is five foot ten, implies that Jones is taller than Smith (cf. Jackson (1998: 3)). It is precisely in this sense that an analysis of sentences semantic properties can be located in an empirical account of the world: semantic is actually being entailed by naturalism. 18

19 less than realism. For one thing, they do not explain why the theories they maintain are mere cognitively meaningless instruments are so successful, how it is that they can make such powerful, successful predictions. Realism explains this very simply by pointing out that the predictions are consequences of the true (or close true) proposition that comprise the theories. (Maxwell 1970: 12) Maxwell obviously submits that statements displaying epistemic virtues are more plausible than those which lack such virtues. Thus, as Psillos (1999: 74 5) indicates, Maxwell gives a Bayesian twist to his argument. Supposing that both realism and instrumentalism entail the empirical success of scientific theories, they will both have likelihoods equal to unity: p(s R) = p(s I) = 1, where R stays for realism, I for instrumentalism, and S for the empirical success of scientific theories. According to Bayes s theorem, the posterior probabilities of realism and respectively, instrumentalism, are p(r S) = p(r)/p(s) p(i S) = p(i)/p(s), where p(r) is the prior probability of realism, p(i) is the prior probability of instrumentalism, and p(s) is the probability of science s success. Certainly, p(s) does not depend on the philosophy of science which accounts for it, so that it has the same value for both realism and instrumentalism. Therefore, p(r S) p(i S) = p(r) p(i) That means that any difference in the degree of confirmation of realism and instrumentalism stems from a difference in their respective priors. 4 Arguing that realism is clearly better supplied with epistemic virtues than realism an idea that many antirealists will, of course, not accept 5 Maxwell infers that the prior probability of realism is much higher than the prior probability of instrumentalism. 4 The reference to prior probabilities underlines the difference from Putnam s NMA, as Wolfgang Spohn (personal correspondence) points out. 5 This line of argument goes exactly opposite to the more popular Popper/van Fraassen inference from the fact that the probability of the observational consequences of any theory is at least equal or higher than the probability of the theory itself, to the conclusion that instrumentalism is generally more probable than realism. I shall have more to say about this in chapter 7, where I shall reject this latter line of argument. 19

20 It will be seen that, in spite of their merits in undermining the credibility of black box instrumentalism, Smart s and Maxwell s arguments are vulnerable when faced with more sophisticated versions of instrumentalism, such as van Fraassen s constructive empiricism. 2.3 The argument from realism s exclusive capacity to give causal explanations My argument for scientific realism stands against instrumentalism and its brethren: phenomenalism, claiming the equivalence of meaning of sentences about physical entities to sentences about sensations; fictionalism and the philosophy of as-if, according to which theories or concepts can be reliably used without for the to be true, or for their terms to refer (they can serve as heuristic fictions or regulative ideas, according to Hans Vaihinger); and constructive empiricism, which will be investigated in detail. Let us proceed by supposing that a given theory T is empirically successful, that is to say, it makes accurate observational predictions. Why does everything happen as if T were true? As we have seen, T s realist supporter typically resorts to the following IBE: if T is a well-established theory, T is empirically successful because the entities it posits exist, and their properties are correctly described by T. Put differently, T s success is explained by T s truthlikeness. In response, the instrumentalist typically advances the following counterarguments: T s empirical success is not in need of any explanation. According to van Fraassen (1980) whose constructive empiricism is an epistemic sort of instrumentalism there is no wonder that scientific theories are successful, because they are the result of natural selection in the jungle of epistemic competition:...science is a biological phenomenon, an activity by one kind of organism which facilitates its interaction with the environment. I claim that the success of current scientific theories is no miracle. It is not even surprising to the scientific (Darwinist) mind. For any scientific theory is born into a life of fierce competition, a jungle red in tooth and claw. Only the successful theories survive the ones which in fact latched on to actual regularities in nature. (van Fraassen 1980: 39 40) Van Fraassen urges us not to ask for the (approximate) truth of theories, but for their empirical adequacy (i.e., for the truth of their observable consequences): Do not ask why the mouse runs from its enemy. Species which did not cope with their natural enemies no longer exist. That is why there are only one who 20

21 do. (van Fraassen 1980: 39). However, it is legitimate to ask why precisely this theory and not a different one has survived in the cruel epistemic jungle. That is, we want to identify some specific feature of the mouse which accounts for what it is that made its behavior fit for survival. We want to know what causes the mouse to run from its enemy. Instead, all that van Fraassen tells us is that the mouse is a survivor because it runs from its enemy. This can barely satisfy our need of an explanation. A different instrumentalist move is motivated by the pragmatist view that the concept of truth should be defined in terms of pragmatic usefulness. The thought entertained by Fine (1991), among others is that in order to explain the empirical success of science, we should not inflate the explanation with any features that go beyond the instrumental reliability of theories. Accordingly, as the instrumentalist proposes, we ought to replace truthlikeness with an epistemically weaker notion, like empirical adequacy or pragmatic usefulness. Nonetheless, in line with Niiniluoto (1999) and Psillos (1999), I argue that such explanatory strategies have the major inconvenience of not explaining at all the practical success of science. To clarify this, let us first write down the typical realist explanatory schemata: T is empirically successful, because T is truthlike. Yet, here is what happens if we replace truthlike with empirically adequate : 6 T is empirically successful, because T is empirically adequate. But empirical adequacy means just the truth of T s observational consequences, i.e. T s empirical success. Consequently, the above explanatory schemata is nothing but an idle tautology: T is empirically adequate, because T is empirically adequate. Therefore, it appears that, following such a strategy, instrumentalism doesn t actually explain at all. Now, to be more true to scientific practice, we ought also to explicitly take into account that, as a matter of fact, instrumentalist attitudes are quite often present in science. As Brian Ellis (1985) states, scientific realists run into trouble when they try to generalize about scientific theories. They tend to make their cases with rather simple historical examples of causal explanations, which urge a realistic understanding as is the case study of atomism, which we discuss in chapter 3. 6 This is a slight adaptation of Niiniluoto s (1999: 197) explanatory sentences. 21

22 However, I argue here in favor of scientific realism and against a general instrumentalist reading of theories, that there is a crucial respect in which the former does systematically better than the latter: it can give causal explanations. For the sake of notational simplicity, let us henceforth call T a realistically interpreted, well-established theory, and T I its instrumentalist restriction to observables. My contention is that, in general, T I cannot offer causal explanations. The argument will be that by systematically rejecting the commitment to the unobservables posited by T, T I frequently blocks our asking why-questions. As Wesley Salmon (1984) puts it, one obvious fact about scientific explanations is its frequent appeal to unobservable entities. We explain diseases in terms of microorganisms....we explain television transmission by appealing to electromagnetic waves which propagate through space. We invoke DNA to explain genetic phenomena. We explain human behavior in terms of neurophysiological processes or, sometimes, in terms of unconscious motives. (Salmon 1984: 206) In line with this view, I seek to establish the thesis that unobservables are essential to the causal structure of the world. Using Salmon s nomenclature, the constituents of the world s causal structure are causal interactions, by which modifications in structure are produced; causal processes, by which structure and order are propagated from one space-time region of the universe to other times and places (1984: 179); and causal laws, which govern the causal processes and interactions, providing regularities that characterize the evolution of causal processes and the modifications that result from causal interactions. (1984: 132). What we typically observe are statistical correlations between events. In one of Salmon s examples, Adams and Baker are students who submitted virtually identical term papers in a course. Undoubtedly, the teacher will be very likely to consider it highly improbable that the papers came out like that by pure chance. Instead he will countenance one of the following reasonable possibilities: (1) Baker copied from Adams, (2) Adams copied from Baker, or (3) both copied from a common source. (Salmon 1984: 207). In other words, There is either (1) a causal process running from Adams s production of the paper to Baker s, (2) a causal process running from Baker s production of the paper to Adams s, or (3) a common cause for example, a paper in a fraternity file to which both Adams and Baker had access. In the case of this third alternative, there are two distinct causal processes running from the paper in the file to each of the two papers submitted by Adams and Baker, respectively. (Salmon 1984: 207) 22

23 Suppose it turns out that (3) is the case. We say then that there is an indirect causal relevance between the considered events: The common cause (the reproduction of the original paper) is connected through causal processes to each of the separate effects. Let T be the theory positing the relevant causal mechanisms. T thus explains causally the statistical correlations between events A and B. In the above example, A and B are the teacher s establishing that Adams and Baker have, respectively, submitted virtually identical papers. All the same, in this case T I (which rejects T s unobservable part) will do as well as T. Since both T and T I account for the correlations between the observable events in terms of observable interactions and observable causal processes, there is no reason not to take T I (instead of T ) as the theory providing the right causal explanation. The same point applies when two events are directly causally relevant to each other, i.e. when A and B are connected by a causal process through which the causal influence is transmitted. This corresponds either to (1) or to (2) in the term-paper example. However, there are many familiar circumstances under which T I s causal explanations clearly fail. Consider the following situation: Someone threw a stone and broke the window. As T I s supporter would have it, it is perfectly all right to take the stone s being thrown as the cause, the motion of the stone through the space as the causal process transmitting the causal influence, and the window s being broken as the effect in an causal connection between observable events. So, after all, T seems to have no monopoly on causal explanations; T I can also explain causally. If this was the case, T I could explain everything that T can, and so would be a priori preferable on grounds of its ontological parsimony. Nonetheless, this construal misunderstands the idea of explaining causally. In the window example, one may legitimately ask, why does a normal windowpane actually break when hit by a stone. T s advocate can (at least try to) locate an event C on the spatiotemporal line going from A to B, C consisting of the absorption of the stone s kinetic energy into the molecular structure of the glass. C screens off A from B, meaning that knowledge of C renders A and B statistically independent (section 3.2 will detail Salmon s statistical analysis). Obviously, C s description must include terminology referring to microphysical entities. To express it differently, although causal explanations can in some cases be given merely by reference to observable events, the former ought to be compatible with underlying causal mechanisms by which some conserved physical quantity is transmitted from the cause to the effect. From this perspective, causal explanations relying only on correlations between observable events, though often satisfactory for common purposes, are in fact mere fragments of more detailed descriptions, given in terms of unobservable causal interac- 23