The Realism/Antirealism Debate in the Philosophy of Science

(1)

The Realism/Antirealism Debate in the Philosophy of

Science

Dissertation

zur Erlangung des akademischen Grades des Doktors der Philosophie (Dr. phil.) an der

Universit¨at Konstanz, Geisteswissenschaftliche Sektion,

Fachbereich Philosophie

vorgelegt von

Radu Dudau

Konstanz, Mai 2002

(2)

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

(6)

claimed to exist. We can picture the existence dimension as a vertical one, having at its lowest level the claim thatsomething 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 6.1ideas– such as numbers, values, propositions, etc., exist, is to adoptabstract 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

(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

(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 aconstitutive 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 ameaning 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 ana- lyzing 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 pointAto pointB”

would be true if and only if electrons were indeed flowing fromAtoB. (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 insemantic instrumentalism,

(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

(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 de- clines 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 theunderdeter- mination 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,

(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, overarch- ing 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.

(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 fi- nancial 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 Kath- leen 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.

(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 un- dergirds 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

1As we shall see in section 2.2, one antirealist argument capitalizes on the alleged insuffi- cient stringency of IBE at the methodological level.

(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

‘aisF’, we can just talk ofa’s approximately beingF. 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 ofscientific 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 callsstrong 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

(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 calltheory 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, de- nouncing them for being context-dependent, inconsistent, and viciously circu- lar. 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 predic- tive 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

(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 isthe 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 onas 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 no- tions. Among others, Laudan (1981) maintains that these are undefined no- tions, 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.

(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 lin- guistic 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)

2I shall henceforth be explicit about the varieties of instrumentalism whenever the distinction is relevant, and the context itself cannot indicate it.

(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. How- ever, 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 in- stantiates 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 competi- tors of realism become more and more convoluted andad hoc and explain

3We should note that many realists are wary of talk of conceptual analysis and a priori reasoning. The so-calledepistemological 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.

(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. Re- alism 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,

whereR stays for realism, I for instrumentalism, andS 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 accept⁵ – Maxwell infers that the prior probability of realism is much higher than the prior probability of instrumentalism.

4The reference to prior probabilities underlines the difference from Putnam’s NMA, as Wolfgang Spohn (personal correspondence) points out.

5This 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.

(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 byT. Put differently, T’s success is explained by T’s truthlikeness.

In response, the instrumentalist typically advances the following counter- arguments: 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

(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. Ac- cordingly, 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, becauseT is truthlike.

Yet, here is what happens if we replace ‘truthlike’ with ‘empirically adequate’:⁶ T is empirically successful, becauseT 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, becauseT 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.

6This is a slight adaptation of Niiniluoto’s (1999: 197) explanatory sentences.

(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, andT_I its instrumentalist re- striction 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 byT,T_I frequently blocks our askingwhy-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 televi- sion 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 pro- duced; causal processes, by which “structure and order are propagated from one space-time region of the universe to other times and places (1984: 179);

andcausal 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)

(23)

Suppose it turns out that (3) is the case. We say then that there is anindirect causal relevance between the considered events: The common cause (the re- production of the original paper) is connected through causal processes to each of the separate effects. LetT be the theory positing the relevant causal mechanisms. T thus explains causally the statistical correlations between eventsA 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 caseT_I (which rejectsT’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 aredirectly 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 TI’s supporter would have it, it is per- fectly 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 thatT 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 window- pane actually break when hit by a stone. T’s advocate can (at least try to) locate an eventC on the spatiotemporal line going from AtoB,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 com- patible 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-

(24)

tions and of transmission of causal influence through continuous spatiotemporal processes. Knowledge of these hidden mechanisms is inherent to scientific investigation. As Philip Dawid (2001) puts it,

such deeper understanding of [the hidden workings of our units] ... is vital for any study of inference about ‘causes of effects’, which has to take into account what has been learned, from experiments, about the inner workings of the black box. (Dawid 2001: 60).⁷

By definition,TI’s defender cannot present a causal process to parallel the one posited byT, since T_I only talks of observables. Thus, T_I’s explanatory capability will not answer many of our legitimate why-questions. T’s explanatory superiority overTI is thus reinstated.

Certainly, antirealists of the Humean tradition will reject causal talk alto- gether. By assuming the existence of causes, my argument seems actually to assume realism. My answer is straightforward: by taking scientific practice at face value, I also assume the legitimacy of causal talk. It is not among the purposes to answer here skepticism about causation.⁸

A different objection is that describing causal relations in terms of underlying unobservable mechanisms is question-begging within the debate about scientific realism. Although antirealists like van Fraassen turn themselves occa- sionally to unobservables for explanatory purposes, they explicitly deny belief in such entities (cf. van Fraassen 1980: 151–2). That is, although van Fraassen turns toT’s theoretical posits for purposes of pragmatic explanation, he does not acceptT as true, but only as empirically adequate. He is agnostic about T’s unobservables.

Again, I shall not delve too much into the details of refuting this objection.

I refer to Kukla’s (1998) own argument, drawing on Friedman (1982) – which

7In the same fragment, Dawid admits that probing into the hidden parts of the causal mechanisms is not necessary for assessing ‘effects of causes’, “which can proceed by an es- sentially ‘black box’ approach, simply modelling dependence on the response on whatever covariate information happens to be observed for the test unit.” (Dawid 2001: 60)

8Note, however, that in the complex task of identifying causal structures from probabilistic relationships among events, supporters of causality are in good company. Judea Pearl (2000), for example, argues in great detail for the advantages of encoding knowledge in causal rather than probabilistic structures. I share with him the intuition that “probabilistic relationships, such as marginal and conditional independencies, may be helpful in hypothesizing initial causal structures from uncontrolled observations. However, once knowledge is cast in causal structure, those probabilistic relationships tend to be forgotten; whatever judgments people express about conditional independencies in a given domain are derived from the causal structure acquired. This explains why people feel confident asserting certain conditional independencies (e.g., that the price of beans in China is independent of the traffic in Los Angeles) having no idea whatsoever about the numerical probabilities involved (e.g., whether the price of beans will exceed $10 per bushel) (Pearl 2000: 25)”.

(25)

will be discussed in detail in 4.8 – showing that it is inconsistent to use the language of T while bracketing (or plainly rejecting) T’s unobservable part.

The argument-line is that if one believes T’s observable consequences, and if the existence of an entity X is among the observable consequences of T, then one must believe in the existence ofX. Consequently,T_I’s defender who accepts T’s unobservables for pragmatic purposes comes eventually to believe in (at least some) unobservables, thus contradicting TI itself.

Let us summarize the steps of the argument:

(1) Well-established theories committed to unobservables, such as T, generally allow the formulation of frameworks for causal, as well as for other – abstract model, functional, and systematic forms of explanation.

(2) T_I precludes the search for causal explanations appealing to unobservables.

(3) Causal explanations appealing to unobservables are essential to scientific investigation.

(4) Therefore, we should always prefer T to TI. T in fact accommodates all above enumerated sorts of explanatory frameworks, while T_I bars, by definition, at least the possibility of explaining causally in terms of unobservables.

Let us now proceed by rejecting a few general criticisms against IBE, which is the pillar of the explanatory defence of realism.

2.4 Van Fraassen’s arguments against IBE

Bas van Fraassen (1984; 1989) has undertaken one of the most original attacks against IBE. From a Bayesian perspective, he maintains that the probability calculus and the requirement that beliefs should be updated by conditionalization provide necessary and sufficient conditions for justified belief. He rejects the view that rationality demands any supplementary ampliative rule to place qualitative constraints on the way in which we update our beliefs. He explicitly views IBE as a paradigm example of such a rule.

Inspired by Kvanvig (1994), we divide van Fraassen’s attack on IBE into two parts, according to the following objections:

(I) IBE is context-dependent, so it probably leads to ‘the best explanation out of a bad lot’.

(II) IBE leads to inconsistency in one’s diachronic probability distribution.

(26)

Let us examine each of them in turn.

2.4.1 The context-dependency objection

Van Fraassen objects that given that the best explanation is always to be selected out of a set of already formulated hypotheses, we cannot warrant that the true hypothesis lies among them. Therefore IBE probably leads to ‘the best of a bad lot’. Moreover, given that the pool of possible explanations is very wide (probably infinite, as the advocates of the underdetermination of theories by empirical data – which will be criticized in chapters 3 and 4 – would have it), and given that we cannot be sure about the truth-value of the best explanatory hypothesis, it follows that the probability of the latter is very low.

Yet, as Niiniluoto points out, a proper Bayesian construal of the problem offers a straightforward solution: “we always consider cognitive problems as sets of mutually exclusive and jointly exhaustive hypotheses.” (1999: 188). In order to exhaust the universe of discourse, one of the hypotheses may be the so-called ‘catch-all’ hypothesis, that is, the negation of all other hypotheses.⁹

A situation may no doubt occur, where none of the presented hypotheses qualifies as an acceptable explanation; it just may not make sense to apply IBE if its outcome has an unacceptably low probability. For such a case, Niiniluoto recommends the suspension of judgement as the most rational thing to do. In order to improve upon this situation, we need to enrich the basis of selection for the best explanation either by acquiring new information, or by introducing concepts more adequate to the object of our explanation.

It is also interesting to note, along with Psillos (1999: 224–225), that if valid, this objection of van Fraassen would be problematic to his own philosophy of science, constructive empiricism. Constructive empiricism takes empirical adequacy – not approximate truth – as the goal of science: when it accepts a theory, it accepts it as empirically adequate, i.e. as true on the observable level. In order to establish the empirical adequacy of a theory, we have to examine an infinite set of empirically equivalents, and pick the empirically adequate one through an ampliative step from the finite evidence. Yet, assuming the validity of van Fraassen’s objection, no such step can be authorized, so belief in the empirical adequacy of a theory cannot be warranted.

In any event, this fact is not directly relevant to van Fraassen’s epistemic criticism against IBE, which will now be pursued.

9The point has also been made by Lipton (1993).

(27)

2.4.2 The inconsistency objection

Van Fraassen (1984, 1989) sets out to demonstrate that the practice of giving a bonus to explanatory hypotheses leads one to accept bets which one is guaranteed to lose. His strategy is based on constructing a Dutch Book strategy – that is, a diachronic Dutch Book – against an agent who, in addition to the classical probability calculus, also adopts IBE as a procedure to update his beliefs.¹⁰

Let us explain the key terminology. ADutch Book is a set of bets offered to an agent by a clever (though mischievous) bookie, bets which have the following characteristics: (i) the bookie who generates them only knows the agent’s degrees of belief; (ii) each of the bets is accepted as fair by the agent;

and (iii) the set of bets guarantees that the bookie will garner a net win.

If an agent is liable to Dutch booking, then his degrees of belief violate the probability axioms.¹¹ For that reason, a necessary condition for rational belief is taken to consist in an immunity to Dutch Books.

Van Fraassen (1989) distinguishes between two varieties of Dutch Books:

synchronicanddiachronic. Synchronic Dutch Books are known as Dutch Book Arguments and consist of sets of simultaneously offered bets, at one moment in time. By contrast, diachronic Dutch Books – known as Dutch Book strategies – rely on the bookie’s option to offer new bets at later moments. As already mentioned, to construct a Dutch Books Argument is equivalent to showing that an agent’s degrees of belief violate the axioms of probability calculus; the agent holds inconsistent beliefs, which is irrational. Yet, it will be shown that the same cannot be said about Dutch strategies: immunity from them is not required for rational belief.

Van Fraassen criticizes IBE for making those who follow it liable to Dutch Book strategies. He (van Fraassen 1989: 166–9) proceeds by imagining a series of bets between Peter and his Bayesian friend, Paul, with respect to a die whose bias of coming upace is not known. Assuming that the first four tosses of the die come upace(propositionE), the bookie (Paul) proposes the following bets concerning the hypothesis H that the fifth toss will be also ace:

Bet I pays $10,000 if E is true and H is false.

Bet II pays $1,300 if E is false.

10More recently (1995), van Fraassen has ceased to rely on Dutch Books as a means to discuss rationality issues.

11As John Earman (1992: 39–40) points out, the Dutch Book theorem proves that if any of the probability axioms is violated, then a Dutch book can be made. TheConverse Dutch Book theorem proves that if the axioms are satisfied, then a Dutch book cannot be made in a finite number of steps. Earman also indicates the difficulties with the Dutch Book justification of the probability axioms.

(28)

Bet III pays $300 if E is true.

The bookie bases his proposal on his knowledge of the fact that Peter has learned IBE from a travelling Preacher (reason for which van Fraassen calls IBE the “Preacher’s Rule”; it says that the posterior probability for each hypothesis of bias depends not only on the initial probabilities and the series of outcomes, but also on their explanatory success). Thus, Paul knows that Peter will assign a higher value to the probability that the fifth toss will also come upace than he would if he only followed Bayesian conditionalization.

Peter assesses the fair costs of the bets on the basis of the outcomes’ probabilities and the offered values. The model used to calculate initial probabilities introduces a factor X of bias, which can take N different forms:

X(1), . . . , X(N). If the die has bias X(I), then the probability of ace on any one toss isI/N. X(N) is the perfect bias, givingace a probability (N/N) = 1 (cf. van Fraassen 1989: 163). In Peter’s model,N = 10:

P(E) equals the average of (.1)⁴, . . . ,(.9)⁴,1, that is.25333.

P(¬E) is.74667.

P(E&¬H) is the average of (.1)⁴(.9), ...(.9)⁴(.1),0, that is.032505.

These probabilities, along with the values of the bets, give the following costs of the bets, which both Peter and the bookie consider to be fair:

The fair cost of bet I is $325.05.

The fair cost of bet II is $970.67.

The fair cost of bet III is $76.00.

The total cost of the bets is $1,371.72. Since he deems them fair, Peter buys them all from his friend. Now, van Fraassen continues, suppose that not all four tosses have come up ace, that is,E is false. So Peter loses bets I and III and wins bet II. In other words, Peter spends a total of $1,371.72 and receives

$1,300. Hence the bookie makes a net gain of $71.72.

IfE has come out true, Peter loses bet II, but has already won bet III, so he gets $300 from the bookie. At this point, bet number I can be formulated as

Bet IV pays $10,000 if H is false.

The bookie proposes to buy this bet from Peter, who agrees to sell it for

$1000, because his probability that the next toss will be anace is, as dictated by Preacher’s Rule,.9. The moment Peter pays $1000 for bet IV, Paul can be happy: even before the fifth toss, he has a guaranteed gain. He paid $300 for

(29)

losing bet III and $1000 for buying bet IV, i.e. $1300, which ensures him a net gain of $71.72.

So, van Fraassen concludes, as a belief-updating rule, IBE leads to inco- herence:

What is really neat about this game is that even Peter could have figured out beforehand what would happen, if he was going to act on his new probabilities. He would have foreseen that by trading bets at fair value, by his own lights, he would be sure to lose $71.72 to his friend, come what may. Thus, by adopting the preacher’s rule, Peter has becomeincoherent – for even by his own lights, he is sabotaging himself. (van Fraassen 1989: 168–9)

Let us now analyze van Fraassen’s argument against IBE. Kvanvig (1994) reconstructs it neatly:

(1) There exists a series of bets, described as bets I–IV above, with a cost as noted above, and that, if taken, guarantee a net loss no matter what happens.

(2) If one is a consistent follower of a particular ampliative rule, one regards this set of bets as fair.

(3) It is irrational to regard such a series of bets as fair.

(4) Therefore, it is irrational to be a consistent follower of the particular ampliative rule that implies than one regards all of the bets in question as fair.

(5) For any ampliative rule, there is a set of bets that are regarded as fair if one consistently follows that ampliative rule which constitutes a Dutch Book strategy.

(6) Therefore, it is irrational to be a consistent follower of any ampliative rule. (Kvanvig 1994: 331)

The weak point of this argument is premise (3). In fact, it is doubtful whether it is true. Moreover, as will be seen, contrary to van Fraassen’s assumption, the bookie actually did cheat against Peter.

Note that not all sets of bets which guarantee a net loss are irrational. To see this, let us consider two categories of bookies with extraordinary powers, whom, inspired by Christensen, we shall term Super-bookies: (i) the Omni- scient Super-bookie, and (ii) the Prescient Super-bookie.

(30)

(i) The Omniscient Super-bookie knows everything. In particular, he knows with certitude the truth-values of every proposition which can make the object of a bet. When buying a bet from him, the only chance of a human fallible agent is to assign a probability of either 0 or 1 to any proposition, and to be correct about it. However, for fallible agents, such a doxastic practice would be irrational. Rationality forbids the ascription in all situations of extreme probability values to the given propositions. Thus, our agent is sure to incur a loss.

(ii) The Prescient Super-bookie is the one who has privileged information about the agent’s probability distribution. More exactly, he knows not only the current probability distribution, but also what changes the agent will make in his degrees of belief over time. Here is what could happen if this was the case:

...suppose the prescient bookie knows that one’s probability forptoday is .7, and also knows that tomorrow it will be .6. In such a case, a series of bets guaranteed to net one a loss is easy to construct: the bookie offers, and you accept, a bet today that pays $10 and costs .7($10) = $7, if p is true, and buys a bet from you that pays $10 if p is true, and costs .6($10) = $6. Then you and your bookie exchange a $10 bill whether or notpis true, resulting in a net profit for the bookie of $1. If this bookie knows your probability will be higher tomorrow than today, he employs the same strategy, this time offering and buying bets on the negation of p. (Kvanvig 1994: 332–3)

Therefore, the agent again is guaranteed a net loss if he buys bets from the Prescient Super-bookie.

The possibility to block such a Dutch Book strategy seems to consist in obeying a strong diachronic condition which precludes any doxastic modifi- cation whatsoever. Christensen labels it the “Calcification” condition. No doubt, Calcification cannot be a reasonable requirement. There are numerous cases in which rationality urges us to modify our credences. For that reason, as Christensen puts it, “we do not think that the beliefs an agent holds at different times should cohere in the way an agent’s simultaneous beliefs should.”

(Christensen 1991: 241). A Dutch strategy would indicate the inconsistency of someone’s set of beliefs only if those beliefs ought to be consistent. Often, in light of new relevant information, we do over time arrive rationally at beliefs contradictory to (not to mentiondifferent from) the earlier ones.

It actually seems that the rational thing to do is simply not to bet against Super-bookies. If an agent did so in spite of information about the extraordinary powers of the bookie, then we say that he acted stupidly. Rationality urges us to be suspicious about such bookies. The point is also expressed by Christensen:

The Realism/Antirealism Debate in the Philosophy of Science