Against Lewisian Modal Realism From a Metaontological Point of View. Tora Koyama, Osaka University, Japan

Transcription

1 Against Lewisian Modal Realism From a Metaontological Point of View Tora Koyama, Osaka University, Japan koyama@irl.sys.es.osaka-u.ac.jp

2 The aim of this talk Modal realism discussed in On the Plurality of s (Lewis 1986) is one of the most notorious theories in metaphysics. It is hard to uphold modal realism, and indeed modal realism has a few advocates. Most metaphysicians agree, however, it is difficult to refute modal realism. I argue against modal realism from a metaontological point of view, thereby I shed light on inherent difficulties of modal realism.

3 Outline 1. A Formulation of Lewisian Modal Realism 2. Lewisian Modal Realism and Ontological Realism 3. Is Ontological and Modal Realism Tenable?

4 1. A Formulation of Lewisian Modal Realism

5 A Formulation Three theses of modal realism: Existence: There exists possible worlds as well as the actual world. Concreteness: Possible worlds are concrete just as the actual world is. Plenitude: Absolutely every way in which the actual world might be is a way in which some possible world is.

6 Reductive Analysis of Modality: A Good Reason for Modal Realism Correspondence: it is possible that p iff there is a possible world w such that 'p' is true at w. Given Correspondence, the truth values of modal statements can be given by the truths at possible worlds, if the following requirements meet: 1.Possible worlds exist. 2.Possible worlds can be characterized without modal notions. 3.There are many enough possible worlds to cover all modal statements.

7 Some Objections Since the purpose of this talk is to shed light on inherent difficulties of modal realism, some objections are put aside: Non-reductivism Modalism (cf. Forbes 1985) Other reductive theories Combinatorialism (cf. Armstrong 1989) Actualism (cf. Adams 1974; Plantinga 1974) Objections to Correspondence

8 2. Metaontology and Lewisian Modal Realism

9 Metaontology What is metaontology? - Ontology is about what there is. - Metaontology is about what is asked by ontological questions. A recent metaontological dispute (Chalmers et al 2009): - Ontological realism vs. Ontological anti-realism

10 Ontological Realism According to ontological realism: - Ontological disputes are substantive. - Ontological questions have determinate answers and are settled by reality. Ontology is an inquiry into the fundamental structure of reality.

11 Ontological Anti-realism According to ontological anti-realism: - Ontological disputes are merely verbal. - Ontological questions have no determinate answers, or at least their answers are settled by not reality but us (our concepts or linguistic conventions, for instance). Ontology is a merely verbal, or at most conceptual or linguistic inquiry.

12 Realism vs. Anti-realism Example: - Special Composition Question: Under what circumstance do many things compose a sum? Universalist: always Nihilist: never Ontological anti-realist: depends on our convention of compose : we could choose to use our language either in a way that many things always compose a sum, or in a way that many things never compose a sum.

13 Two Problems From Ontological Anti-realism Non-substantivity: According to ontological anti-realism, we might use our language either in a way in which Existence is true or in a way in which Existence is false. Question about the theses of modal realism is not substantive. Failure of Reduction: According to ontological anti-realism, we might use our language in a way in which Plenitude is false. Whether the reduction of modality succeeds or fails depends on our linguistic conventions.

14 Fundamentality Modal realism can incorporate ontological realism by appealing to the notion of fundamentality. Fundamental is often used to conciliate the anti-realistic intuition and ontological realism. - "The most interesting ontological question is not the question of what exists, but is rather the question of what is fundamental. (Schaffer 2009b) Although different versions of fundamentality has been proposed in metaontology, I focus on Schaffer s version for simpilicity.

15 Schafferian Ontological Realism Ontological questions are trivial because everything exists. There is an elite class of things, that is, things that are fundamental. Ontology is an inquiry into what is fundamental. Definition of fundamentality: x is fundamental iff nothing grounds x. The basic relation of ground(ing) is primitive and supposed to be irreflexive, asymmetric, and transitive.

16 Schafferian Ontological Realism : the grounding relation What is fundamental is what lies at the bottom of the grounding relation. The grounding relation is primitive and supposed to be irreflexive, asymmetric, and transitive. Fundamental Entities

17 Three Requirements No-Collapse: Distinction between what is and what is not fundamental dose not collapse, meaning that it is neither the case that everything is fundamental, nor is it the case that everything is not fundamental. Determinacy: The distinction is determinate and settled by reality rather than our linguistic conventions or conceptions. Ontological Reflection: Ontological status of entities reflects how fundamental they are, as opposed to whether they exist or not.

18 Schafferian Answer To Failure of Reduction: Existence and Plenitude are determinately true simply because everything exists. There is no room for Failure of Reduction. To Non-substantivity: While the questions of what exists is non-substantive (since everything exist), the question of what is fundamental is substantive because of No-Collapse and Determinacy.

19 How to Make Modal Realism Ontologically Realistic Four theses of O-modal realism: Existence: There exists possible worlds as well as the actual world. Concreteness: Possible worlds are concrete just as the actual world is. Plenitude: Absolutely every way in which the actual world might be is a way in which some possible world is. Fundamentality: Possible worlds are fundamental.

20 Summery of Part 2 Metaontology is about what is asked by the ontological questions. There is a metaontological debate between ontological realism and anti-realism. If modal realism accepts ontological anti-realism, two problems arise: Non-substantivity and Failure of Reduction. If modal realism incorporates ontological realism, it can avoid the two problems by appealing to the notion of fundamentality. In order to make modal realism ontologically realistic, it is sufficient to simply accept the additional thesis of the fundamentality of possible worlds.

21 3. Is Ontological and Modal Realism Tenable?

22 Impossible s Impossible worlds are too similar with possible worlds to be treated separately. In other words, whenever there is a reason to consider one, there is a similar reason to consider the other. For instane, utility is a reason to consider possible worlds: Given that possible worlds are used widely, their ontological status should be theorized. Utility Argument for Impossible s: Since impossible worlds are used not only in metaphysics, but also in other areas of philosophy, their ontological status should be theorized.

23 Problem of Impossible s To treat possible world and impossible worlds separetely, non-circular characterization of possible worlds is needed. However, it would be highly problematic for O-modal realism. Modal realism is promising because other reductive theories of modality need primitive modality while modal realism does not. This would be questioned if the non-circular characterization obtains. For instance, ersatz modal realism could argue that ersatz possible worlds would not need primitive modalty because of the non-circular characterization.

24 Only way out? If there is no difference in ontological status between possible and impossible worlds, the problem of how to draw a line between them will vanish. Acceptance of impossible wolrds as well as possible wolrds is a well-known position in the debate on impossible worlds (cf. Yagisawa 1988; 2010). Extended modal realism: impossible worlds exists as well as possible worlds.

25 Extending O-Modal Realism Four theses of E-modal realism: E-Existence: There exists the actual and other worlds including impossible worlds. E-Concreteness: Other worlds, including impossible ones, are concrete just as the actual world is. E-Plenitude: Absolutely every way in which the actual world might or might not be is a way in which some other world is. E-Fundamentality: All worlds are fundamental.

26 Argument Against E-Modal Realism Given No-Collapse, there must be something that is not fundamental. The simplest idea is that all entities other than worlds are not fundamental. It is easy to derive a characterizaion if we accept Lewisian definition of possible worlds accoding to which worlds are maximal sums of spatiotemporally related things: Mereological characterization of fundamentality: x is fundamental iff x is a proper part of any other thing that is spatiotemporally related with it.

27 Monism like E-Modal Realism The mereplogical characterization makes E-modal realism similar with priority monism (Schaffer 2009a). I call this version of E-modal realism Monism-like E-modal realism. Monism-like E-modal realism is characterized by two additional theses: Lewisian s: s are maximal sums of spatiotemporary related things. Sum-Priority: Sums are more fundamental than their proper parts.

28 Problem of Junky Junky world is a world such that there is no maximal sum of spatiotemporally related things in it. Definition of Junky : A world w is junky iff everything in w is a proper part of some other thing therein. Since the actual world might (or might not) have been a junky world, there is a junky world, according to E-Plenitude. A junky world is problematic because there are no fundamental entities in a junky word since there is no maximal sum therein.

29 Junky Even impossibility of junky worlds can make a hole in the realm of fundamentals.

30 Nihilism like E-Modal Realism A way to avoid the problem is junky world is to shift the focus from possible worlds to possibilia. This suggests a different version of E- modal realism. I call it Nihilism-like E-modal realism. Nihilism-like E-modal realism is obtained by replacing E- Fundamentality with the following thesis: Atom-Fundamentality: Only the smallest parts of worlds are fundamental. It needs to replace Sum-Priority with the following thesis: Part-Priority: Sums are less fundamental than their proper parts.

31 Problem of Gunky Gunky world is a world that has no smallest parts. Definition of Gunky : A world w is gunky iff everything in w has a proper part. Since the actual world might (or might not) have been a gunky world, there is a gunky world, according to E- Plenitude. A gunky world is problematic because there are no fundamental entities in a gunky word since it has no smallest parts.

32 Gunky

33 Even impossibility of gunky worlds can make a hole in the realm of fundamentals.

34 Summery of Part 3 1.Problem of Impossible s: O-modal realists cannot treat possible worlds and impossible worlds separately since if they can, their advantage over other theories would be questioned. Only way out is to accept E-modal realism. 2.Argument Against E-modal realism: There must be something that is not fundamental, but if worlds and fundamentality are defined mereologically, there must be a world without fundamental entities, according to E-Plenitude.

35 Conclusion

36 Summary From a metaonotlogical point of view, Lewsian modal realism should incorporate ontological realism. Being ontological realism, Lewsian modal realism needs to offer a way to determinately distinguish fundamentals and non-fundamentals. It is quite difficult because no matter how they are distinguished, a possibility (or impossibility) always remains that there are no such fundamentals. Thus, it contradicts Plenitude, one of the central theses of Lewsian modal realism.

37 Concluding Remarks O-modal realism must give a distinction between fundamentals and non-fundamentals in a way that is settled by reality. The problem of junky or gunky world suggests that this requirement cannot be met without rejecting Plenitude. Many critic find Plenitude is the most problematic among the principles concerning Lewiston modal realism. What I have added is that there is no way to maintain Plenitude if metaontological considerations are taken into account. If Lewsian modal realism does not incorporate ontological realism, either the question of existence of possible worlds is not substantive, or the advantage over other reductive theories is denied. Either way, we are justified in paying much less attention to modal realism than we have done before.