What Are Impossible Worlds?

Philosophy Compass, 2009

It is difficult to wander far in contemporary metaphysics without bumping into talk of possible worlds. And reference to possible worlds is not confined to metaphysics. It can be found in contemporary epistemology and ethics, and has even made its way into linguistics and decision theory. What are those possible worlds, the entities to which theorists in these disciplines all appeal? This paper sets out and evaluates a leading contemporary theory of possible worlds, David Lewis's Modal Realism. I note two competing ambitions for a theory of possible worlds: that it be reductive and user-friendly. I then outline Modal Realism and consider objections to the effect that it cannot satisfy these ambitions. I conclude that there is some reason to believe that Modal Realism is not reductive and overwhelming reason to believe that it is not user-friendly.

Analysis, 1984

auslegung: a journal of philosophy

Journal of Philosophical Logic, 2012

Among the most remarkable developments in metaphysics since the 1950's is the explosion of philosophical interest in possible worlds. This paper proposes an explanation of what possible worlds are, and argues that this proposal, the interpreted models conception, should be attractive to anyone who thinks that modal facts are primitive, and so not to be explained in terms of some non-modal notion of "possible world." I articulate three constraints on any acceptable primitivist explanation of the nature of possible worlds, and show that the interpreted models conception meets the three constraints. there were and what they were like. 1 Providing a non-modal explanation of the notion of being a possible world has occupied center stage in the thought of these philosophers. It will not, however, occupy center stage here. We are not going to require here that the notion of being a possible world be explained in thoroughly non-modal terms. Suppose, then, that modal primitivism is true: some modal facts cannot be reduced to, or even explained in terms of, any congeries of exclusively non-modal facts. Even granting that (SC) does not provide fodder for an explanation of modal facts in non-modal terms, there remain a number of alternative views of (SC)'s significance. One could suggest, for instance, that instances of (SC) are simply meaningless, since they all crucially employ the notion of being a possible world, and that notion has not been explained. Alternatively, one could simply deny that there are any possible worlds. Then there will be instances of (SC)-those involving true possibility claims-that are false. If we take either of these skeptical lines, then much of contemporary modal metaphysics will turn out to be either meaningless or a pack of falsehoods. And other disciplines that make liberal use of possible worlds, e.g. some strands of linguistics, ethics, epistemology, and decision theory, will suffer from the same defect. 2 This need not imply that talk of possible worlds in all of these

2014

The authors provide an object-theoretic analysis of two paradoxes in the theory of possible worlds and propositions stemming from Russell and Kaplan. After laying out the paradoxes, the authors provide a brief overview of object theory and point out how syntactic restrictions that prevent object-theoretic versions of the classical paradoxes are justified philosophically. The authors then trace the origins of the Russell paradox to a problematic application of set theory to define worlds. Next the authors show that an object-theoretic analysis of the Kaplan paradox reveals that there is no genuine paradox at all, as the central premise of the paradox is simply a logical falsehood and hence can be rejected on the strongest possible grounds --- not only in object theory but for the very framework of propositional modal logic in which Kaplan frames his argument. The authors close by fending off a possible objection that object theory avoids the Russell paradox only by refusing to incorporate set theory and, hence, that the object theoretic solution is only a consequence of the theory's weakness.

Annals of the Japan Association for Philosophy of Science, 1983

Kripke seems generally accepted nowadays. It states in essence that a sentence is necessarily true if it is true not only in the real world but also in all "possible worlds". In the following I will attempt to give a new formal explication of the concept of necessity. This concept will be identified as the concept of logical necessity, for only the latter seems sufficiently clear.

2013

The paper outlines and immediately discusses the so-called 'soft' impossibility, i.e., non-logical impossibility generated by modal realism. It will be shown that although in a particular case genuine modal realism, straightforwardly applied, deems impossible a proposition that other philosophers have claimed to be (intuitively) possible, there is a variety of methodologically acceptable moves available in order to avoid the problem. The impossibility at issue is the existence of island universes. Given the Lewisian analysis there are three points at which we might try to square genuine modal realism with such a controversial and problematic claim of (im)possibility, namely: a) the contraction of our pre-theoretical opinions about possibility, b) the revision of some Lewisian definitions and/or c) the extension of our ontological commitments. I shall look at each of these approaches applied to the problematic case.

The Journal of Philosophy, 1988

An Empire of Thin Air (1988) David Lewis's book, On the Plurality of Worlds, is derived from his 1984 John Locke Lectures, and is the latest word on possible worlds from the discipline's foremost champion of possibilia. It is a serious defense, a priori, of Lewis's notorious doctrines (here called 'modal realism') to the effect that there are tiny purple anthropologists who study human culture unobserved, colossal human-eating monsters 50 feet in height, professional philosophers earning annual salaries in excess of 37 million dollars (pre-inflation), and the like, and that these oddities reside in fabulous alternative universes that are never empirically detected by us (but that are empirically detectable by us). The central idea of Lewis's theory is that whatever might have transpired involving individuals of our universe does indeed transpire in one of these alternative universes, involving counterparts of these individuals (p. 2)-'the principle of plenitude.' Equally critical to Lewis's project is the converse principle that everything that transpires in one of these alternative universes involving our counterparts is something that might have transpired involving ourselves. We may call this 'the principle of moderation.' 1 Together these two principles assert an isomorphism between total ways things might have been with regard to this universe and extant alternative universes, prompting Lewis to identify the former with the latter (p. 86). Lewis thus misleadingly calls his alleged alternative universes 'possible worlds,' and indeed they play a role in Lewis's theory of modal discourse similar in many respects to that of the intensional possible worlds invoked in contemporary philosophical semantics, as conceived of by such writers as Saul Kripke and Robert Stalnaker, that is, maximally specific states or histories. 2 These genuine possible worlds Lewis misleadingly labels 'ersatz worlds.' Like genuine possible worlds, Lewis's alternative universes allegedly 'represent' possible events and states of affairs that might have occurred concerning the individuals of our universe; they are supposed to be entities according to which 1 These principles are not explicitly articulated as I have them. My statement of plenitude is based on a plausible interpretation of Lewis's less explicit formulation. Lewis provides a version of moderation which is closely related to, but much weaker than, the principle formulated here, and which he derives from the trivial modal logical truth that whatever is the case might have been the case (p. 5). This weaker principle, however, is insufficient for Lewis's purposes.

The Quasi-Truth theory offered an important formal approach to the understanding both partiality scientific knowledge – through the so called " partial structures " – so a theory capable of dealing with the notion of " pragmatic truth ". Some important notions that we find in scientific works that scapes from the formal treatment offered by the theory of quasi-truth are modal notions as, for example, necessity, possibility and counterfactual statements. In this work we intend to develop a possible worlds semantics for the Quasi-Truth theory, by preserving the approach of both partiality of scientific and pragmatic truth, but also offering an interpretation for modal operators. Within this formalism, we shall show that we can get several different modal systems. Generally speaking, our aim is to reach to a theory that comprises the concept of quasi-truth and that is able to treat modality as is applied to scientific theories.

1991

Abstract Recently, the relationship between several forms of default reasoning based on conditional defaults has been investigated. In particular, the systems based on ε-semantics, preferential models, and (fragments of) modally-defined conditional logics have been shown to be equivalent. These systems form a plausible core for default inference, but are too weak in general, failing to deal adequately with irrelevance.