Constructive empiricism implies that if van Fraassen does not believe that scientific theories and his positive philosophical theories, including his contextual theory of explanation, are empirically adequate, he cannot accept them, and hence he cannot use them for scientific and philosophical purposes. Moreover, his epistemic colleagues, who embrace epistemic reciprocalism, would not believe that his positive philosophical theories are empirically adequate. This epistemic disadvantage comes with practical disadvantages in a social world.

Constructive empiricism, the view introduced in The Scientific Image, is a view of science, an answer to the question "what is science?" Arthur Fine's and Paul Teller's contributions to this symposium challenge especially two key ideas required to formulate that view, namely the observable/unobservable and acceptance/belief distinctions. I wish to thank them not only for their insightful critique but also for the support they include. For they illuminate and counter some misunderstandings of Constructive Empiricism along the (...) way. That leaves me free to focus on those two main challenges. (shrink)

Constructive empiricism is not just a view regarding the aim of science; it is also a view regarding the epistemological framework in which one should debate the aim of science. This is the focus of this book -- not with scientific truth, but with how one should argue about scientific truth.

Constructive empiricism - as formulated by Bas van Fraassen - makes no epistemological claims about the nature of science. Rather, it is a view about the aim of science, to be situated within van Fraassen's broader voluntarist epistemology. Yet while this epistemically minimalist framework may have various advantages in defending the epistemic relevance of constructive empiricism, I show how it also has various disadvantages in maintaining its internal coherence.

It is argued that, contrary to prevailing opinion, Bas van Fraassen nowhere uses the argument from underdetermination in his argument for constructive empiricism. It is explained that van Fraassen’s use of the notion of empirical equivalence in The Scientific Image has been widely misunderstood. A reconstruction of the main arguments for constructive empiricism is offered, showing how the passages that have been taken to be part of an appeal to the argument from underdetermination should actually be (...) interpreted. (shrink)

James Ladyman has argued that constructive empiricism entails modal realism, and that this renders constructive empiricism untenable. We maintain that constructive empiricism is compatible with modal nominalism. Although the central term 'observable' has been analyzed in terms of counterfactuals, and in general counterfactuals do not have objective truth conditions, the property of being observable is not a modal property, and hence there are objective, non-modal facts about what is observable. Both modal nominalism and (...) class='Hi'>constructive empiricism require clarification in the face of Ladyman's argument. But we also argue that, even if Ladyman were right that constructive empiricism entails modal realism, this would not be a problem for constructive empiricism. (shrink)

constructive empiricism asserts that it is not for science to reach a verdict on whether a theory is true or false, if the theory is about unobservable entities; science's only interest here, says Van Fraassen, is to discover whether the theory is ‘empirically adequate’. However, if a theory is soley about observables, empirical adequacy and truth are said to ‘coincide’, here discovering the theory's truth value is an appropriate scientific goal. Constructive empiricism thus rests an epistemological (...) thesis on a semantical distinction. This paper critically examines the notion of aboutness and its epistemological significance. * I am grateful to members of my philosophy of science seminar during Spring, 1983 for useful discussion and to the two anonymous referees of this journal for providing helpful suggestions. I also thank the University of Wisconsin, Madison Graduate School for support in the form of a Romnes Faculty Fellowship. (shrink)

In this paper, I argue that Constructive Empiricism (CE) is ambiguous between two interpretations: CE as a normative epistemology of science and CE as a descriptive philosophy of science. When they present CE, constructive empiricists write as if CE is supposed to be more than a normative epistemology of science and that it is meant to be responsible to actual scientific practices. However, when they respond to objections, constructive empiricists fall back on a strictly normative interpretation (...) of CE. This ambiguity seems to make CE immune to objections in a rather ad hoc fashion. (shrink)

In this paper I will set out my understanding of Bas van Fraassen’s constructive empiricism, some of the difficulties which I believe beset the current version, and, very briefly, some valuable lessons I believe are nonetheless to be learned by considering this view.We’ll need to begin with a review of how van Fraassen conceives of this kind of discussion.

Constructive Empiricism, the view introduced in The Scientific Image, is a view of science, an answer to the question “what is science?” Arthur Fine’s and Paul Teller’s contributions to this symposium challenge especially two key ideas required to formu- late that view, namely the observable/unobservable and accept- ance/belief distinctions. I wish to thank them not only for their insightful critique but also for the support they include. For they illuminate and counter some misunderstandings of Constructive Empiricism (...) along the way. That leaves me free to focus on those two main challenges. The three of us share a good deal of common history. So it is perhaps only remarkable, and not astonishing, that we now share a common leaning to Pragmatism in philosophy. Of us three I am clearly themost conservative in this respect, especially as pertaining to truth, reference, and belief.2 Arthur Fine showed very nicely how Constructive Empiricism could have been conceived under the canopy of Dewey’s Instrumentalism. Much of it could appear as a Corollary to that sort of Instrumentalism, I agree. But in fact Iwould not be happy to land in that general Pragmatist position. (shrink)

, I argued that Bas van Fraassen's constructive empiricism was undermined in various ways by his antirealism about modality. Here I offer some comments and responses to the reply to my arguments by Bradley Monton and van Fraassen [2003]. In particular, after making some minor points, I argue that Monton and van Fraassen have not done enough to show that the context dependence of counterfactuals renders their truth conditions non-objective, and I also argue that adopting modal realism does (...) after all undermine the motivation for constructive empiricism. Introduction Underdetermination and epistemic modesty Counterfactual observations Modal realism and constructive empiricism. (shrink)

In this paper, I argue that, contrary to the constructive empiricist’s position, observability is not an adequate criterion as a guide to ontological commitment in science. My argument has two parts. First, I argue that the constructive empiricist’s choice of observability as a criterion for ontological commitment is based on the assumption that belief in the existence of unobservable entities is unreasonable because belief in the existence of an entity can only be vindicated by its observation. Second, I (...) argue that the kind of ontological commitment that is under consideration when accepting a scientific theory is commitment to what I call theoretical kinds and that observation can vindicate commitment to kinds only in exceptional cases. (shrink)

Constructive empiricists claim to offer a reconstruction of the aim and practice of science without adopting all the metaphysical commitments of scientific realism. Deflationists about truth boast of the ability to offer a full account of the nature of truth without adopting the metaphysical commitments accompanying substantive accounts. Though the two views would form an attractive package, I argue that the pairing is not possible: constructive empiricism requires a substantive account of truth. I articulate what sort of (...) account of truth and empirical adequacy the constructive empiricist must offer and then show why deflationists cannot uphold such an account. (shrink)

Bas van Fraassen maintains that the actual function of optical instruments is producing images. Still, the output of a telescope is different from that of a microscope, for in the latter case it is not possible to empirically investigate the geometrical relations between the observer, the image and the detected entity, while in the former it is - at least in principle. In this paper I argue that this is a weak argument to support the belief in the existence of (...) exoplanets that, according to van Fraassen, comes with accepting a theory that posits these entities. If a constructive empiricist asserts the empirical adequacy of such a theory, she might be relying on typical realist arguments, instead - of the very same ilk as the ones used to defend the veridicality of microscopic images. Perhaps the time has come for van Fraassen to explain his view on telescopes. (shrink)

James Ladyman ([2000]) argues that constructive empiricism is untenable because it cannot adequately account for modal statements about observability. In this paper, I attempt to resist Ladyman's conclusion, arguing that the constructive empiricist can grant his modal discourse objective, theory-independent truth-conditions, yet without compromising his empiricism.

According to Bas van Fraassen, a postulated entity which can only be detected by means of some instrument should not be considered observable. In this paper I argue that (1) this is not correct; (2) someone can be a constructive empiricist, adhering to van Fraassen’s famous anti-realist position, even admitting that many entities only detectable with a microscope are observable. The case of the paramecium, a very well-known single-celled organism, is particularly instructive in this respect. I maintain that we (...) actually observe paramecia and not just detect them, contrary to what van Fraassen claims. As a matter of fact, even if we can only perceive these protozoans by using a microscope, we are in condition to know that the relevant counterfactual conditions (like the ones Bueno proposed in 2011) are met. Moreover, paramecia satisfy observability and existence criteria proposed by Buekens (1999) and Ghins (2005). But admitting paramecia and the like among the observables does not threaten Constructive Empiricism, for there will always be a line between observables and unobservables on which van Fraassen’s anti-realism can rest. (shrink)

Constructive empiricism, Bas van fraassen's new variety of anti-Realism, Maintains that science aims at empirically adequate, Rather than true theories and that, In fully accepting a theory, One should believe only that it is empirically adequate. A theory is empirically adequate just in case it has a model in which all observable phenomena may be embedded. I challenge van fraassen's main arguments and argue that the observable/unobservable distinction will not bear the weight that van fraassen places on it.

Van Fraassen's constructive empiricism is presently the most influential and well-developed alternative to scientific realism. In this paper I argue that a reasonable condition on the distinction between belief and agnosticism prevents van Fraassen from claiming that we can be agnostic about what a theory says about unobservable entities while simultaneously accepting that theory. The upshot is that we must find some other way to do justice both to the argument for constructive empiricism and to van (...) Fraassen's cogent criticisms of scientific realism. I suggest that a highly attractive alternative is founded upon semantic anti-realism, and that empiricists should develop this alternative. (shrink)

According to van Fraassen, constructive empiricism (CE) makes better sense of scientific activity than scientific realism (SR). I discuss a recent episode in biomedical research - investigations about Helicobacter Pylori and its relation to peptic ulcer. CE's expedient to cope with it is a sort of belief substitution. I argue that replacing realist beliefs by empiricist surrogates (as-if beliefs) could accommodate scientists' expectations and behavior. Nonetheless, theoretical agnosticism could hardly motivate scientists to focus just on the observational consequences (...) derived from the theory at issue. Contrary to van Fraassen, I conclude then that, concerning scientific practice, realist beliefs cannot be considered as a gratuitious surplus which should be rejected. (shrink)

One of the most common criticisms one hears of the idea of granting a legitimate role for social values in theory choice in science is that it just doesn’t make sense to regard social preferences as relevant to the truth or to the way things are. “What is at issue,” wrote Susan Haack, is “whether it is possible to derive an ‘is’ from an ‘ought.’ ” One can see that this is not possible, she concludes, “as soon as one expresses (...) it plainly: that propositions about what states of affairs are desirable or deplorable could be evidence that things are, or are not, so” (Haack 1993a, 35, emphasis in original). The purpose of this chapter is not to determine whether this widespread view is correct, but rather to show that even if we grant it (which I do), we may still consistently believe that social values have a legitimate role in theory choice in science. I will defend this conclusion by outlining a view about social values and theory choice that is available to a Constructive Empiricist anti-realist, but not to a realist. (shrink)

Van Fraassen defines constructive empiricism as the view that science aims to produce empirically adequate theories. But this account has been misunderstood. Constructive empiricism in not, as it seems, a description of the intentional features of scientific practice, nor is it a normative prescription for their revision. It is rather a fiction about the practice of science that van Fraassen displays in the interests of a broader empiricism. The paper concludes with a series of arguments (...) designed to show that constructive empiricism so understood is self-undermining. (shrink)

In this paper, I argue that the “positive argument” for Constructive Empiricism (CE), according to which CE “makes better sense of science, and of scientific activity, than realism does” (van Fraassen 1980, 73), is an Inference to the Best Explanation (IBE). But constructive empiricists are critical of IBE, and thus they have to be critical of their own “positive argument” for CE. If my argument is sound, then constructive empiricists are in the awkward position of having (...) to reject their own “positive argument” for CE by their own lights. (shrink)

Over the past years, in books and journals (this journal included), N. Maxwell launched a ferocious attack on B. C. van Fraassen’s view of science called Constructive Empiricism (CE). This attack has been totally ignored. Must we conclude from this silence that no defence is possible and that a fortiori Maxwell has buried CE once and for all? Or is the attack too obviously flawed as not to merit exposure? A careful dissection of Maxwell’s reasoning will make it (...) clear that neither is the case. This dissection includes an analysis of Maxwell’s ‘aberrance–argument’ (omnipresent in his many writings) for the claim that science implicitly and permanently accepts a substantial, metaphysical thesis about the universe, which then paves the way for his own metaphysical-realist hierarchy-view of science. This aberrance-claim, which Maxwell directs against a widely shared and harmful ideology of science called ‘Standard Empiricism’, generally has been ignored too, for more than a quarter of a century. Our conclusions will be that (i) Maxwell’s attacks on CE can be beaten off, and (ii) his ‘aberrance–arguments’ do not establish what Maxwell believes they establish, but (iii) we can draw a number of valuable lessons from these attacks about the nature of science and of the libertarian nature of CE. (shrink)

In this paper I articulate a fictionalist solution to the closure problem that affects constructive empiricism. Relying on Stephen Yablo’s recent study of closure puzzles, I show how we can partition the content of a theory in terms of its truthmakers and claim that a constructive empiricist can believe that all the observable conditions that are necessary to make a part of her theory true obtain and remain agnostic about whether or not the other truthmakers for the (...) other parts of her theory obtain. This can be done even though she asserts her theory as if it was wholly true. (shrink)

I begin chapter I by discussing two key distinctions that constitute the core of van Fraassen's constructive empiricism: a distinction between observables and unobservables and a distinction between acceptance and belief with regard to a theory. To support constructive empiricism, van Fraassen also deploys two epistemological principles: only actual observations are to be taken as evidence and possible evidence is all that can be rationally inferred from the actual evidence. I reject both principle and van Fraassen's (...) construal of observation. As does van Fraassen, I make the distinction between acceptance and belief in chapter II. I contend that one does not need to be an antirealist to espouse this distinction between acceptance and belief. ;In the remaining chapters, I develop a quasi-Bayesian account of acceptance as an alternative to van Fraassen's. In chapter III, I consider three views of acceptance: van Fraassen's, Bayesian views, and the epistemic view. I argue that both van Fraassen's account and the epistemic account are open to Bayesian objections. However, Bayesianism assumes a controversial principle called "maximization of expected utility" , which might mitigate the impact of the Bayesian objections. ;In the final chapter, I consider different decision principles, e.g. Kyburg's decision principle, and Gardenfors and Sahlin's decision principle. I formulate a decision principle called the "weak-dominance-decision principle " based on Kyburg's theory . The interval-based probability yields, as a limiting case, the point-valued probability when we have complete information about the event in question. In this case, my decision principle reduces to MEU. Therefore, the same Bayesian objections against both van Fraassen's theory of acceptance and the epistemic theory of acceptance could be made from the perspective of my decision principle while escaping the perils of strict Bayesianism. My theory of acceptance is quasi-Bayesian, because WDP rests on interval-based probability. (shrink)

No doubt my earlier paper has struck a sensitive nerve among existing and prospective constructive empiricists – hence their united reply.1 I shall, for brevity, introduce an imaginary single author of their critique and call him CE. In this rejoinder, I try to show, first, that CE’s counter-arguments do not refute my original arguments; and second, that a claim of CE’s paper is very close to the conclusion of my original paper. A central point of my original piece was (...) that there is a symmetry between scientific realism and constructive empiricism vis à vis van Fraassen’s arguments from the bad lot and from indifference. Scholastic charges of an ‘apparent misunderstanding’ of ‘empirical adequacy’ do not cast any light on the issues at stake. (However, the notion of empirical adequacy I employed, p. 41, is the standard one: ‘a theory is empirically adequate if and only if it saves all phenomena, past, present and future, and squares with all actual and possible observations’.) The issue between CE and myself is more substantive: CE relies on the thesis that for any theory there are ‘indefinitely many empirically equivalent rivals’ (p. 307), in order to infer that there are infinitely many empirically adequate theories, and then to argue that if realists.. (shrink)

Manifestationalism holds that science aims only to give us theories that are correct about what has been observed thus far. Several philosophers, including Bas van Fraassen, have argued that manifestationalism cannot make sense of the scientific impetus to make new observations, since such observations only risk turning manifestationally adequate theories into inadequate ones. This paper argues that a strikingly similar objection applies to van Fraassen’s own constructive empiricism, the view that science aims only to find theories that are (...) empirically adequate. Roughly, the objection is that constructive empiricism cannot make sense of the scientific impetus to expand the limits of what can be observed, since such expansions only risk turning empirically adequate theories into inadequate ones. (shrink)

In response to parts I-III of G Rosen's "What is Constructive Empiricism?", "Philosophical Studies", 74, 1994, 143-178, this paper examines several construals of the position of constructive empiricism. At issue, in part, is the equation of intentional aspects of science with the intentions and opinions of scientists. In addition it is necessary to distinguish the constructive empiricist -- a philosopher holding that acceptance of theories in science need not involve belief that they are true -- (...) from the scientific agnostic' who accepts but does not believe current science. What is at stake for empiricism is a view of science that will admit it as a paradigm for rational inquiry. (shrink)

Van Fraassen stresses two distinct but interrelated themes in The Scientific Image: the semantic view of theories and the epistemic status of unobservables. The first of these could easily be accepted by a scientific realist, and indeed realists like Giere have already adapted it to their purposes. So the specifically empiricist thread in van Fraassen’s philosophy stems from the second.Van Fraassen breaks from tradition in founding his empiricism not on the ontological status of unobservable entities but on the epistemic (...) attitude we take to them. The main points of his position are these:1)The claims of scientific theories, including claims about unobservable entities, are to be taken literally. Theories are not reconstructed so as to remove claims of the existence of unobservable objects.2)Observation is a matter of direct observation by accepted participants in the human scientific community. (shrink)

This paper addresses the question: how should the traditional doxastic attitude of agnosticism be represented in a Bayesian framework? Bas van Fraassen has one proposal: a Bayesian is agnostic about a proposition if her opinion about the proposition is represented by a probability interval with zero as the lower limit. I argue that van Fraassen's proposal is not adequate. Mark Kaplan claims that this leads to a problem with constructive empiricism; I show that Kaplan's claim is incorrect.

Alan Musgrave, Michael Friedman, Jeffrey Foss, and Richard Creath raised different objections against the Distinction between observables and unobservables when drawn within the confines of Bas C. van Fraassen's Constructive Empiricism, to the effect that the Distinction cannot be drawn there coherently. Van Fraassen has only responded to Musgrave but Musgrave claimed not to understand van Fraassen's succinct response. I argue that van Fraassen's response is not enough. What remains in the end is an unsolved problem which CE (...) cannot afford to leave unsolved, or so I argue; I then strengthen Musgrave's criticism and indicate that an extension of the epistemic policy of CE is mandatory to solve the problem. I also argue that Friedman's and Foss' objection against the Distinction in CE misses the mark on closer inspection. An objection due to Creath does hit the mark but can be taken care of without too much ado. All these objections seem alive and kicking until the present day; I try to put them all to rest. (shrink)

Constructive empiricism, the scientific anti-realism championed by Bas van Fraassen, claims to offer an adequate reconstruction of the aim and practice of scientific inquiry without adopting the inflationary metaphysical excesses of scientific realism. In articulating the positions of the realist and the empiricist, van Fraassen freely makes use of the concept of truth. Theories of truth come in a variety of flavors, some more metaphysically stark than others. Deflationary theories of truth, for instance, boast of the ability to (...) offer a full account of the nature of truth without having to succumb to the supposed metaphysical extravagances accompanying more substantive accounts. Constructive empiricism and deflationism about truth seem, then, to form a natural pair. My contention is that such a pairing is not possible— constructive empiricism requires a more substantive account of truth than can be offered by the deflationist. (shrink)

By focussing on the intentional character of observation in science, we argue that Constructive Empiricism—B.C. van Fraassen’s much debated and explored view of science—is inconsistent. We then argue there are at least two ways out of our Inconsistency Argument, one of which is more easily to square with Constructive Empiricism than the other.

Astroparticle physics is an interdisciplinary field embracing astronomy, astrophysics and particle physics. In a recent paper on this topic, Brigitte Falkenburg defended that only scientific realism can make sense of it and that realist beliefs constitute an indispensable methodological principle of research in this discipline. The aim of this work is to show that there exists an anti-realist alternative to this account, along the lines of what Bas van Fraassen showed in his famous book The Scientific Image. Problems and results (...) of astroparticle physics can be understood from an empiricist point of view too, namely that of van Fraassen’s constructive empiricism, which is a more modest and metaphysics-free alternative to scientific realism. Although constructive empiricism can make sense of science no worse than scientific realism does, van Fraassen’s goal is not to demonstrate that his stance is the only viable position, but just that it is not incoherent or proven false by his opponents. In this paper it will be shown that the constructive empiricist stance constitutes a legitimate alternative to scientific realism even when it gets to astroparticle physics and that it does indeed make sense of this new discipline, pace Falkenburg. (shrink)

This reassessment of the long debate about Friedman's thesis on the pointlessness of testing assumptions in economics shows that Friedman's three famous examples, on which a large part of the credit given to this thesis is based, far from substantiating it, can be used to establish radically opposite conclusions. Furthermore, it is shown that this so-called “instrumentalist” thesis, when applied by Friedman to economics, is of a quite different nature and raises much more serious problems than the standard instrumentalist thesis (...) devised by some methodologists of physics. To disentangle these ambiguities concerning realism and instrumentalism applied to physics or to economics, this paper refers to Van Fraassen's “constructive empiricism”, which is helpful in reformulating, in a more satisfactory way, the essentials of Friedman's considerations about empiricism and anti-realism. (shrink)

In this paper, I explore Rosen’s ‘transcendental’ objection to constructive empiricism—the argument that in order to be a constructive empiricist, one must be ontologically committed to just the sort of abstract, mathematical objects constructive empiricism seems committed to denying. In particular, I assess Bueno’s ‘partial structures’ response to Rosen, and argue that such a strategy cannot succeed, on the grounds that it cannot provide an adequate metalogic for our scientific discourse. I conclude by arguing that (...) this result provides some interesting consequences in general for anti-realist programmes in the philosophy of science.Keywords: Constructive empiricism; Mathematical fictionalism; Partial structures; Modality. (shrink)

Bas van Fraassen claims that constructive empiricism strikes a balance between the empiricist’s commitments to epistemic modesty – that one’s opinion should extend no further beyond the deliverances of experience than is necessary – and to the rationality of science. In “Should the Empiricist be a Constructive Empiricist?” I argued that if the constructive empiricist follows through on her commitment to epistemic modesty she will find herself adopting a much more extreme position than van Fraassen suggests. (...) Van Fraassen and Bradley Monton have recently responded. My purpose here is to contest their response. The goal is not merely the rebuttal of a rebuttal; there is a lesson to learn concerning the realist/anti-realist dialectic generated by van Fraassen’s view. (shrink)

According to constructive empiricists, accepting a scientific theory involves belief only that it is true of the observable world, where observability is defined in terms of what is detectable by the unaided senses. On this view, scientific instruments are machines that generate new observable data, but this data need not be interpreted as providing access to a realm of phenomena beyond what is revealed by the senses. A recent challenge to the constructive empiricist account of instruments appeals to (...) the extended mind thesis, according to which cognitive processes are sometimes constituted not just by brain activity, but can extend into the rest of the body and the surrounding environment. If this is right, scientific instruments may, in the right circumstances, literally become part of our perceptual processes. In this article, I examine this extended perception argument, and I find that it fails for the vast majority of scientific instruments. Even if the extended mind thesis is accepted, the constructive empiricist can draw a line between observables and unobservables that makes very few concessions to the realist. (shrink)

A defence of constructive empiricism against an attack of N. Maxwell by means of his pet-thesis that science implicitly and permanently accepts a metaphysical thesis about the nature of the universe. We argue that Maxwell's attack can be beaten off; that his arguments do not establish what Maxwell believes they establish; and that we can draw a number of valuable lessons from these attacks about the nature of science and of the libertatian nature of constructive empiricism.

Progress in elementary particle physics in recent decades has changed the status of the visible phenomena in the context of scientific research. Empiricist positions in philosophy of science, which put particular emphasis on the pre-eminence of the visible regime, are affected by this development. In spite of its less radical claims, constructive empiricism turns out to run into more serious problems than straightforward instrumentalism. The constructive empiricist’s emphasis on the scientist’s aims makes it essential for her to (...) provide a satisfactory motivation for scientific inquiry. This, however, seems difficult to achieve on an empiricist basis in the case of elementary particle physics. (shrink)

Constructive empiricism is supposed to offer a positive alternative to scientific realism that dispenses with the need for metaphysics. I first review the terms of the debate before arguing that the standard objections to constructive empiricism are not decisive. I then explain van Fraassen's views on modality and counterfactuals, and argue that, because constructive empiricism recommends on epistemological grounds belief in the empirical adequacy rather than the truth of theories, it requires that there be (...) an objective modal distinction between the observable and the unobservable. This conclusion is incompatible with van Fraassen's empiricism. Finally I explain some further problems for constructive empiricism that arise when we consider modal matters. (shrink)

Notice that I’m not saying that observations we in fact have made are not relevant to our beliefs about what exists. But the mere fact that something is observable does not give us any reason to think that it ever has or will in fact be observed. The issue between us is whether mere observability—as distinct from actual observation—is relevant to our beliefs about what exists. I submit that it is not.