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 in the definition of 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. (shrink)

This book is a defense of modal realism; the thesis that our world is but one of a plurality of worlds, and that the individuals that inhabit our world are only a few out of all the inhabitants of all the worlds. Lewis argues that the philosophical utility of modal realism is a good reason for believing that it is true.

This article defends the principle of sufficient reason (PSR) from a simple and direct valid argument according to which PSR implies that there is a truth that explains every truth, namely an omni-explainer. Many proponents of PSR may be willing to bite the bullet and maintain that, if PSR is true, then there is an omni-explainer. I object to this strategy by defending the principle that explanation is irreflexive. Then I argue that proponents of PSR can resist the conclusion that (...) there is an omni-explainer by denying that explanation distributes over conjunction. In the final section, I consider a plausible revision of this assumption. I argue there that, given the revised assumption, PSR seems to yield a striking picture of the explanatory structure of the universe. I explain why the resulting model does not appear utterly implausible to me. (shrink)

The Principle of Sufficient Reason says that all contingent facts must have explanation. In this 2006 volume, which was the first on the topic in the English language in nearly half a century, Alexander Pruss examines the substantive philosophical issues raised by the Principle Reason. Discussing various forms of the PSR and selected historical episodes, from Parmenides, Leibnez, and Hume, Pruss defends the claim that every true contingent proposition must have an explanation against major objections, including Hume's imaginability argument and (...) Peter van Inwagen's argument that the PSR entails modal fatalism. Pruss also provides a number of positive arguments for the PSR, based on considerations as different as the metaphysics of existence, counterfactuals and modality, negative explanations, and the everyday applicability of the PSR. Moreover, Pruss shows how the PSR would advance the discussion in a number of disparate fields, including meta-ethics and the philosophy of mathematics. (shrink)

In this classic, exciting, and thoughtful text, Metaphysics , Peter van Inwagen examines three profound questions: What are the most general features of the world? Why is there a world? and What is the place of human beings in the world? Metaphysics introduces to readers the curious notion that is metaphysics, how it is conceived both historically and currently. The author's work can serve either as a textbook in a university course on metaphysics or as an introduction to metaphysical thinking (...) for the interested reader. This second edition, revised though not fundamentally changed, includes the basis of the first edition with a new chapter on the nature of time. (shrink)

"This is an important book, and no one interested in issues which touch on the free will will want to ignore it."--Ethics. In this stimulating and thought-provoking book, the author defends the thesis that free will is incompatible with determinism. He disputes the view that determinism is necessary for moral responsbility. Finding no good reason for accepting determinism, but believing moral responsiblity to be indubitable, he concludes that determinism should be rejected.

In one of its versions, the principle of sufficient reason maintains that every true proposition has a sufficient reason for its truth. Recently, a number of philosophers have argued against the principle on the ground that there are propositions such as the conjunction of all truths that are ‘too big’ to have a sufficient reason. The task of this article is to show that such maximal propositions pose no threat to the principle. According to what is perhaps the most ‘popular’ (...) version of the principle to sufficient reason (PSR), every true proposition has a sufficient reason why it is true. Peter van Inwagen formulates the principle as follows: ‘for every truth, for everything that is so, there is a sufficient reason for its being true or being so.’ Like many contemporary philosophers, however, he rejects the principle. My purpose here is to show that the main philosophical argument against PSR rests on a mistaken assumption. There is also a ‘scientific’ argument against PSR that turns on considerations of quantum indeterminacy; but that argument lies beyond the scope of this discussion. (shrink)

We look at recent accounts of the indefinite extensibility of the concept set and compare them with a certain linguistic model of indefinite extensibility. We suggest that the linguistic model has much to recommend over alternative accounts of indefinite extensibility, and we defend it against three prima facie objections.

Bertrand Russell offered an influential paradox of propositions in Appendix B of The Principles of Mathematics, but there is little agreement as to what to conclude from it. We suggest that Russell's paradox is best regarded as a limitative result on propositional granularity. Some propositions are, on pain of contradiction, unable to discriminate between classes with different members: whatever they predicate of one, they predicate of the other. When accepted, this remarkable fact should cast some doubt upon some of the (...) uses to which modern descendente of Russell's paradox of propositions have been put in recent literature. (shrink)

Bringsjord (1985) argues that the definition W of possible worlds as maximal possible sets of propositions is incoherent. Menzel (1986a) notes that Bringsjord’s argument depends on the Powerset axiom and that the axiom can be reasonably denied. Grim (1986) counters that W can be proved to be incoherent without Powerset. Grim was right. However, the argument he provided is deeply flawed. The purpose of this note is to detail the problems with Grim’s argument and to present a sound alternative argument (...) for his conclusion – basically the argument Russell gave to establish a well-known paradox in The Principles of Mathematics. (shrink)

Metaphysical rationalism, the doctrine which affirms the Principle of Sufficient Reason (the PSR), is out of favor today. The best argument against it is that it appears to lead to necessitarianism, the claim that all truths are necessarily true. Whatever the intuitive appeal of the PSR, the intuitive appeal of the claim that things could have been otherwise is greater. This problem did not go unnoticed by the great metaphysical rationalists Spinoza and Leibniz. Spinoza’s response was to embrace necessitarianism. Leibniz’s (...) response was to argue that, despite appearances, rationalism does not lead to necessitarianism. This paper examines the debate between these two rationalists and concludes that Leibniz has persuasive grounds for his opinion. This has significant implications both for the plausibility of the PSR and for our understanding of modality. (shrink)

Unlike explanation in science, explanation in mathematics has received relatively scant attention from philosophers. Whereas there are canonical examples of scientific explanations, there are few examples that have become widely accepted as exhibiting the distinction between mathematical proofs that explain why some mathematical theorem holds and proofs that merely prove that the theorem holds without revealing the reason why it holds. This essay offers some examples of proofs that mathematicians have considered explanatory, and it argues that these examples suggest a (...) particular account of explanation in mathematics. The essay compares its account to Steiner's and Kitcher's. Among the topics that arise are proofs that exploit symmetries, mathematical coincidences, brute-force proofs, simplicity in mathematics, merely clever proofs, and proofs that unify what other proofs treat as separate cases. (shrink)

Discusses the incompatibility of the concepts of free will and determinism and argues that moral responsibility needs the doctrine of free will.

After briefly reviewing the standard set-theoretic resolutions of the Burali-Forti paradox, we examine how the paradox arises in set theory formalized with plural quantifiers. A significant choice emerges between the desirable unrestricted availability of ordinals to represent well-orderings and the sensibility of attempting to refer to ‘absolutely all ordinals’ or ‘absolutely all well-orderings’. This choice is obscured by standard set theories, which rely on type distinctions which are obliterated in the setting with plurals. Zermelo's attempt ( 1930 ) to secure (...) ordinal representability of arbitrary well-orderings through relativization of quantification to set-theoretic models is reviewed and found wanting. The natural modal-structural recasting provides, it is claimed, a good repair. (shrink)

We argue that certain modal questions raise serious problems for a modal metaphysics on which we are permitted to quantify unrestrictedly over all possibilia. In particular, we argue that, on reasonable assumptions, both David Lewis's modal realism and Timothy Williamson's necessitism are saddled with the remarkable conclusion that there is some cardinal number of the form ℵα such that there could not be more than ℵα-many angels in existence. In the last section, we make use of similar ideas to draw (...) a moral for a recent debate in meta-ontology. (shrink)

This chapter explores an objection to explanatory universalism, the doctrine that the principle of sufficient reason is true or everything has an explanation. This objection is a direct argument to the conclusion that the PSR yields the existence of an omni-explainer, i.e. something that explains everything. The objection crucially relies on the assumption that explanation is dissective in its explanandum place, and its conclusion conflicts with the irreflexivity of explanation. So the chapter considers two responses to the mentioned objection. The (...) first response consisting in restricting the irreflexivity of explanation is criticised in connection with topics in the metaphysics of grounding. The second response consisting in denying that explanation is dissective is vindicated. Finally, the chapter argues that a plausible revised version of the principle that explanation is dissective, the PSR, and the irreflexivity of explanation together yield a striking picture of our universe. (shrink)

A Cantorian argument that there is no set of all truths. There is, for the same reason, no possible world as a maximal set of propositions. And omniscience is logically impossible.

Solutions to Russell’s paradox of propositions and to Kaplan’s paradox are proposed based on an extension of von Neumann’s method of avoiding paradox. It is shown that Russell’s ‘anti-Cantorian’ mappings can be preserved using this method, but Kaplan’s mapping cannot. In addition, several versions of the Epimenides paradox are discussed in light of von Neumann’s method.

"With an astonishing erudition... and in a direct no-nonsense style, Bennett expounds, compares, and criticizes Spinoza’s theses.... No one can fail to profit from it. Bennett has succeeded in making Spinoza a philosopher of our time." --W. N. A. Klever, _Studia Spinoza_.

Published in 1903, this book was the first comprehensive treatise on the logical foundations of mathematics written in English. It sets forth, as far as possible without mathematical and logical symbolism, the grounds in favour of the view that mathematics and logic are identical. It proposes simply that what is commonly called mathematics are merely later deductions from logical premises. It provided the thesis for which _Principia Mathematica_ provided the detailed proof, and introduced the work of Frege to a wider (...) audience. In addition to the new introduction by John Slater, this edition contains Russell's introduction to the 1937 edition in which he defends his position against his formalist and intuitionist critics. (shrink)

This book is an exploration of philosophical questions about infinity. Graham Oppy examines how the infinite lurks everywhere, both in science and in our ordinary thoughts about the world. He also analyses the many puzzles and paradoxes that follow in the train of the infinite. Even simple notions, such as counting, adding and maximising present serious difficulties. Other topics examined include the nature of space and time, infinities in physical science, infinities in theories of probability and decision, the nature of (...) part/whole relations, mathematical theories of the infinite, and infinite regression and principles of sufficient reason. (shrink)

There are four broad grounds upon which the intelligibility of quantification over absolutely everything has been questioned—one based upon the existence of semantic indeterminacy, another on the relativity of ontology to a conceptual scheme, a third upon the necessity of sortal restriction, and the last upon the possibility of indefinite extendibility. The argument from semantic indeterminacy derives from general philosophical considerations concerning our understanding of language. For the Skolem–Lowenheim Theorem appears to show that an understanding of quanti- fication over absolutely (...) everything (assuming a suitably infinite domain) is semantically indistinguishable from the understanding of quantification over something less than absolutely everything; the same first-order sentences are true and even the same first-order conditions will be satisfied by objects from the narrower domain. From this it is then argued that the two kinds of understanding are indistinguishable tout court and that nothing could count as having the one kind of understanding as opposed to the other. (shrink)

This paper presents an argument for the Principle of Sufficient Reason, the PSR, the principle according to which each thing that exists has an explanation. I begin with several widespread and extremely plausible arguments that I call explicability arguments in which a certain situation is rejected precisely because it would be arbitrary. Building on these plausible cases, I construct a series of explicability arguments that culminates in an explicability argument concerning existence itself. This argument amounts to the claim that the (...) PSR is true. The plausibility of the initial cases in the series provides the basis of an argument for the PSR, an argument that can be rebutted only by drawing a line between the plausible early cases in the series and the apparently unacceptable later cases. I argue that no principled reason for drawing this line has been found and that one cannot draw an unprincipled or arbitrary line without begging the question. The paper concludes that, therefore, this defense of the PSR remains unrebutted and that we have a powerful, new reason to embrace the PSR. (shrink)