Descartes was certain that he was thinking and he was accordingly certain that he existed. Like Descartes, we seem to be more certain of our thoughts and our existence than of anything else. What is less clear is the reason why we are thus certain. Philosophers throughout history have provided different interpretations of the cogito, disagreeing both on the kind of thoughts it characterizes and on the reasons for its cogency. According to what we may call the empiricist interpretation of (...) the cogito, I can only claim to be certain of having experiences, and this certainty, as well as that of my own existence, stems from their phenomenal and subjective character. According to rationalist interpretations, on the other hand, I am certain of having some self-reflexive propositional attitudes, and this certainty derives from their rational features. Psychiatric patients suffering from acute forms of depersonalization or of the Cotard syndrome often doubt that they think and exist, and might even believe that they don't. I argue that their study allows us to favor the empiricist interpretation of the cogito. (shrink)

This chapter gives an exposition and critique of Anselm's Proslogion II argument.

This is the text of my OBO entry on arguments for the existence of God.

I propose and defend a surprisingly simple yet useful analysis of existence according to which existence is a relation between a thing and a set: a thing x bears the relation of existence to a set S if and only if x is a member of S . This simple set-theoretic analysis of existence demystifies existence and is powerful and flexible enough to serve important theoretical purposes.

Latest version of my SEP entry on ontological arguments, which first appeared in 1996. General discussion of ontological arguments. Includes a brief historical overview, a taxonomy of different kinds of ontological arguments, a brief survey of objections to the different kinds of ontological arguments identified in the taxonomy, and more extended discussions of Anselm's ontological argument (Proslogion 2), Godel's ontological argument, and Plantinga's ontological argument.

This paper investigates the logic of Ockhamism, a view according to which future contingents are either true or false. Several attempts have been made to give rigorous shape to this view by defining a suitable formal semantics, but arguably none of them is fully satisfactory. The paper draws attention to some problems that beset such attempts, and suggests that these problems are different symptoms of the same initial confusion, in that they stem from the unjustified assumption that the actual course (...) of events must be represented in the semantics as a distinguished history, the Thin Red Line. (shrink)

I critically examine Cappelen and Lepore’s definition of and tests for indexicality, and refine them to improve their adequacy. Indexicals cannot be defined as expressions with different referents in different contexts unless linguistic meaning and circumstances of evaluation are held constant. I show that despite Cappelen and Lepore’s claim that there are only a handful of indexical expressions, their “basic set” includes a number of large and open classes, and generates an infinity of indexical phrases. And while the tests can (...) be used effectively to combat contextualism concerning ‘knows’ and ‘actual,’ many expressions not in their basic set test positive for indexicality, including quantifier nouns, weather reports, and comparative adjectives. I rebut their claim that context-shifting arguments inevitably lead to radical contextualism, and that if there were any indexicals beyond their basic set, communication would be impossible. (shrink)

A fairly simple theory of the semantics of tense is obtained by combining three claims: (i) for any time t, a present-tense sentence `p' is either true or false at t; (ii) for any time t0 earlier than t, the future-tense sentence `It will be the case that p at t' is true at t0 if `p' is true at t, false otherwise; (iii) for any time t0 later than t, the past-tense sentence `It was the case that p at (...) t' is true at t0 if `p' is true at t, false otherwise. This theory, which has been called the theory of timeless truth, is often dismissed on the basis of its alleged incapacity to comply with indeterminism. Here, instead, it will be suggested that there is no reason to be dismissive. Section 1 provides some elucidations about the theory. Sections 2 and 3 explain how a foregone objection to it can be resisted. Sections 4 and 5 show that there is a plausible sense in which (i)-(iii) are compatible with indeterminism. Sections 6 and 7 dispel some misunderstandings that may lead to think that indeterminism is not vindicated in some important sense other than that outlined. (shrink)

In this entry I present one of the most hotly debated issues in contemporary analytic philosophy regarding the nature of fictional entities and the motivations that might be adduced for and against positing them into our ontology. The entry is divided in two parts. In the first part I offer an overview of the main accounts of the metaphysics of fictional entities according to three standard realist views, fictional Meinongianism, fictional possibilism and fictional creationism. In the second part I describe (...) two main kinds of arguments for or against positing fictional entities into our ontology. The first kind is traditionally inspired by the linguistic data coming from our talk about fictional characters. The second kind is more recent and it builds on genuine ontological considerations. (shrink)

The book offers a novel approach to the idea of divinity in guise of a philosophical doctrine called 'Logical Pantheism', according to which the only way to establish the existence of God undeniably is by equating God with Logical Space.

There is a long-standing disagreement among Branching-Time theorists. Even though they all believe that the branching representation accurately grasps the idea that the future, contrary to the past, is open, they argue whether this representation is compatible with the claim that one among many possible futures is distinguished—the single future that will come to be. This disagreement is paralleled in an argument about the bivalence of future contingents. The single, privileged future is often called the Thin Red Line. I reconstruct (...) the history of the arguments for and against this idea. Then, I propose my own version of the Thin Red Line theory which is immune to the major objections found in the literature. I argue that the semantic disagreement is grounded in distinct metaphysical presuppositions. My solution is expressed in a conceptual framework proposed by John MacFarlane, who distinguishes semantics from postsemantics. I extend his distinction and introduce a new notion of presemantics to elucidate my idea. (shrink)

The core of Kant’s criticism of the ontological argument is the thesis that existence is not a real predicate capable of being added to the concept of an object. The concept of the most perfect or the most real being is a subjective content that is as such completely determined, that is to say, that already has all the determinations that define that concept as such. Therefore, to know if that object also exists in the real world is indispensable that (...) the subject has an intuition of it. The absence of such intuition is, according to Kant, an insuperable obstacle for the different attempts to prove the existence of God. Although Hegel agrees in principle with Kant´s claim that existence must not be conceived as a real predicate, he considers, however, that to understand it as the position of the already exhaustively determined concept of the object does not imply a true overcoming of the particular notion of existence that is at the base of the ontological argument. In this article I defend the claim that Hegel´s counter-criticism of Kant´s criticism of the ontological argument is actually a radicalization of Kant´s general critique of metaphysics. (shrink)

Oppenheimer & Zalta have re-formulated their non-modal version of the ontological argument, with the help of PROVER9, an automated reasoning engine. The authors end up rejecting the new argument; however, the theist has a rejoinder worth considering. But after presenting the rejoinder, I highlight that the conceivability of the being does not imply its possibility. One lesson is that even non-modal ontological arguments must engage modal matters concerning God. Another lesson is that if PROVER9 is able to derive a conclusion (...) from fewer premises, the proof is sometimes inferior as an argument. (shrink)

Over the past few years, the tree model of time has been widely employed to deal with issues concerning the semantics of tensed discourse. The thought that has motivated its adoption is that the most plausible way to make sense of indeterminism is to conceive of future possibilities as branches that depart from a common trunk, constituted by the past and the present. However, the thought still needs to be further articulated and defended, and several important questions remain open, such (...) as the question of how actuality can be understood and formally represented in a branching framework. The present volume is intended to be a 360 degree reflection on the tree model. The contributions is gathers concern the model and its alternatives, both from a semantic and from a metaphysical point of view. ​. (shrink)

We outline a theory of the cognitive role of belief in absolute necessity that is normative and intended to be metaphysically neutral. We take this theory to be unique in scope since it addresses simultaneously the questions of how such belief is (properly) acquired and of how it is (properly) manifest. The acquisition and manifestation conditions for belief in absolute necessity are given univocally, in terms of complex higher-order attitudes involving two distinct kinds of supposition (A-supposing and C-supposing). It is (...) subsequently argued that the proposed acquisition and manifestation conditions are rationally interdependent, and that such harmony affords explanations of connections between different facets of belief in necessity that otherwise remain mysterious. (shrink)

In his metaphysical summa of 1986, The Plurality of Worlds, David Lewis famously defends a doctrine he calls ‘modal realism’, the idea that to account for the fact that some things are possible and some things are necessary we must postulate an infinity possible worlds, concrete entities like our own universe, but cut off from us in space and time. Possible worlds are required to account for the facts of modality without assuming that modality is primitive – that there are (...) irreducibly modal facts. We argue that on one reading, Lewis’s theory licenses us to assume maverick possible worlds which spread through logical space gobbling up all the rest. Because they exclude alternatives, these worlds result in contradictions, since different spread worlds are incompatible with one another. Plainly Lewis’s theory must be amended to exclude these excluders. But, we maintain, this cannot be done without bringing in modal primitives. And once we admit modal primitives, bang goes the rationale for Lewis’s modal realism. (shrink)

David Wallace has given a decision-theoretic argument for the Born Rule in the context of Everettian quantum mechanics. This approach promises to resolve some long-standing problems with probability in EQM, but it has faced plenty of resistance. One kind of objection charges that the requisite notion of decision-theoretic uncertainty is unavailable in the Everettian picture, so that the argument cannot gain any traction; another kind of objection grants the proof’s applicability and targets the premises. In this article I propose some (...) novel principles connecting the physics of EQM with the metaphysics of modality, and argue that in the resulting framework the incoherence problem does not arise. These principles also help to justify one of the most controversial premises of Wallace’s argument, ‘branching indifference’. Absent any a priori reason to align the metaphysics with the physics in some other way, the proposed principles can be adopted on grounds of theoretical utility. The upshot is that Everettians can, after all, make clear sense of objective probability. 1 Introduction2 Setup3 Individualism versus Collectivism4 The Ingredients of Indexicalism5 Indexicalism and Incoherence5.1 The trivialization problem5.2 The uncertainty problem6 Indexicalism and Branching Indifference6.1 Introducing branching indifference6.2 The pragmatic defence of branching indifference6.3 The non-existence defence of branching indifference6.4 The indexicalist defence of branching indifference7 Conclusion. (shrink)

Stewart Cohen’s New Evil Demon argument raises familiar and widely discussed concerns for reliabilist accounts of epistemic justification. A now standard response to this argument, initiated by Alvin Goldman and Ernest Sosa, involves distinguishing different notions of justification. Juan Comesaña has recently and prominently claimed that his Indexical Reliabilism (IR) offers a novel solution in this tradition. We argue, however, that Comesaña’s proposal suffers serious difficulties from the perspective of the philosophy of language. More specifically, we show that the two (...) readings of sentences involving the word ‘justified’ which are required for Comesaña’s solution to the problem are not recoverable within the two-dimensional framework of Robert Stalnaker to which he appeals. We then consider, and reject, an attempt to overcome this difficulty by appeal to a complication of the theory involving counterfactuals, and conclude the paper by sketching our own preferred solution to Cohen’s New Evil Demon. (shrink)

Abstract MacFarlane distinguishes “context sensitivity” from “indexicality,” and argues that “nonindexical contextualism” has significant advantages over the standard indexical form. MacFarlane’s substantive thesis is that the extension of an expression may depend on an epistemic standard variable even though its content does not. Focusing on ‘knows,’ I will argue against the possibility of extension dependence without content dependence when factors such as meaning, time, and world are held constant, and show that MacFarlane’s nonindexical contextualism provides no advantages over indexical contextualism. (...) The discussion will shed light on the definition of indexicals as well as the meaning of ‘knows,’ and highlight important constraints on the way meaning can be represented in semantics. Content Type Journal Article Pages 1-14 DOI 10.1007/s11098-011-9831-1 Authors Wayne A. Davis, Georgetown University, Washington, DC, USA Journal Philosophical Studies Online ISSN 1573-0883 Print ISSN 0031-8116. (shrink)

John MacFarlane has recently presented a novel argument in support of truth- relativism. According to this, contextualists fail to accommodate retrospective reassessments of propositional contents, when it comes to languages which are rich enough to express actuality. The aim of this note is twofold. First, it is to argue that the argument can be effectively rejected, since it rests on an inadequate conception of actuality. Second, it is to offer a more plausible account of actuality in branching time, along the (...) line of Lewis (1970/1983). (shrink)

Two-dimensional semantics is a theory in the philosophy of language that provides an account of meaning which is sensitive to the distinction between necessity and apriority. Usually, this theory is presented in an informal manner. In this thesis, I take first steps in formalizing it, and use the formalization to present some considerations in favor of two-dimensional semantics. To do so, I define a semantics for a propositional modal logic with operators for the modalities of necessity, actuality, and apriority that (...) captures the relevant ideas of two-dimensional semantics. I use this to show that some criticisms of two-dimensional semantics that claim that the theory is incoherent are not justified. I also axiomatize the logic, and compare it to the most important proposals in the literature that define similar logics. To indicate that two-dimensional semantics is a plausible semantic theory, I give an argument that shows that all theorems of the logic can be philosophically justified independently of two-dimensional semantics. (shrink)

Chapter III of Anselm's Proslogion is quite naturally interpreted as presenting a second version of the ontological argument. In recent discussions it has been so interpreted by Charles Hartshorne and by Norman Malcolm. Other writers, however, have rejected this interpretation, maintaining that Anselm intended Chapter Ill, not as a second proof of God's existence, but only as a demonstration that the kind of existence which God has is necessary existence. Perhaps the latter writers are correct on this exegetical point, but (...) even so, it does not follow that there is anything improper about an inquiry into the character of the distinct, modal version of the ontological argument which can be derived from this passage. (shrink)

'You ask me about the idiosyncrasies of philosophers? There is their lack of historical sense, their hatred of even the idea of becoming, their Egyptianism. They think they are doing a thing honour when they dehistoricize it, sub specie aeternitatis — when they make a mummy of it.'Nietzsche, Twilight of the Idols.

David Lewis has shocked the philosophical community with his original version of extreme modal realism according to which “every way that a world could possibly be is a way that some world is”. Logical Space is a plenitude of isolated physical worlds, each being the actualization of some way in which a world could be, that bear neither spatiotemporal nor causal relations to each other. Lewis has given independent, converging arguments for this. One is the argument from the indexicality of (...) actuality, the other an elaborate cost-benefit argument of the inference-to-the-best explanation sort to the effect that a systematic analysis of a number of concepts, including modality, causality, propositions and properties, fares better under his theory than under any rival one that takes a possible world to be either a linguistic entity or an ersatz abstract entity such as a maximal compossible set of properties, propositions or states of affairs. Lewis' legion of critics have confined themselves mostly to attempts at a reductio ad absurdum of his theory or to objections to his various analyses. The indexical argument, on the other hand, has not been subject to careful critical scrutiny. It is the purpose of this paper to show that this argument cannot withstand such scrutiny. Its demise, however, leaves untouched his argument from the explanatory superiority for his extreme modal realism. (shrink)

Lewisian Genuine Realism about possible worlds is often deemed unable to accommodate impossible worlds and reap the benefits that these bestow to rival theories. This thesis explores two alternative extensions of GR into the terrain of impossible worlds. It is divided in six chapters. Chapter I outlines Lewis’ theory, the motivations for impossible worlds, and the central problem that such worlds present for GR: How can GR even understand the notion of an impossible world, given Lewis’ reductive theoretical framework? Since (...) the desideratum is to incorporate impossible worlds into GR without compromising Lewis’ reductive analysis of modality, Chapter II defends that analysis against objections. The rest of the thesis is devoted to incorporating impossible worlds into GR. Chapter III explores GR-friendly impossible worlds in the form of set-theoretic constructions out of genuine possibilia. Then, Chapters IV-VI venture into concrete impossible worlds. Chapter IV addresses Lewis’ objection against such worlds, to the effect that contradictions true at impossible worlds amount to true contradictions tout court. I argue that even if so, the relevant contradictions are only ever about the non-actual, and that Lewis’ argument relies on a premise that cannot be nonquestion- beggingly upheld in the face of genuine impossible worlds in any case. Chapter V proposes that Lewis’ reductive analysis can be preserved, even in the face of genuine impossibilia, if we differentiate the impossible from the possible by means of accessibility relations, understood non-modally in terms of similarity. Finally, Chapter VI counters objections to the effect that there are certain impossibilities, formulated in Lewis’ theoretical language, which genuine impossibilia should, but cannot, represent. I conclude that Genuine Realism is still very much in the running when the discussion turns to impossible worlds. (shrink)

The paper is an investigation into the concept of actuality from the standpoint of the philosophy of language. It is argued that expressions such as 'actually' and 'in fact' are not indexicals like 'here' and 'now'; when e.g. 'Snow is actually white' is uttered in a world, what proposition is conveyed does not depend on the world. Nor are such expressions ambiguous. The paper makes a suggestion about the role that 'actually' and its cognates do play. It is also argued (...) that the sentence ⌜Actually S ⌝ expresses a necessary truth only if S itself expresses one. In order to capture the necessitation of the proposition expressed in ⌜Actually S ⌝, it is not sufficient to prefix the word 'necessarily'. (shrink)

The most famous objection to the ontological argument is given in Kant's dictum that existence is not a real predicate. But it is not obvious how this slogan is supposed to relate to the ontological argument. Some, most notably Alvin Plantinga, have even judged Kant's dictum to be totally irrelevant to Anselm's version of the ontological argument. In this paper I argue, against Plantinga and others, that Kant's claim is indeed relevant to Anselm's argument, in the straightforward sense that if (...) the claim is true, then Anselm's argument is unsound. (shrink)

John MacFarlane explores how we might make sense of the idea that truth is relative. He provides new, satisfying accounts of parts of our thought and talk that have resisted traditional methods of analysis, including what we mean when we talk about what is tasty, what we know, what will happen, what might be the case, and what we ought to do.

There is a common approach to metaphysical disputes, which takes language as its starting point, and leads to a view about the range of acceptable metaphysical positions in any such dispute. I argue that this approach rests on accepting what I call the Strong Linguistic Thesis (SLT). In the metaphysical debate about time I argue that the new B-theory has rejected SLT, and for good reasons. The metaphysical debate about modality parallels the early metaphysical debate about time. I argue that (...) a position analogous to the new B-theory of time is available in the modal debate, and has some advantages over its rivals. (shrink)

If a counterpart theorist’s understanding of the counterpart relation precludes haecceitist differences between possible worlds, as David Lewis’s does, how can he admit haecceitist possibilities, as Lewis wants to? Lewis (Philosophical Review 3–32, 1983; On the Plurality of Worlds, 1986) devised what he called a ‘cheap substitute for haecceitism,’ which would allow for haecceitist possibilities while preserving the counterpart relation as a purely qualitative one. The solution involved lifting an earlier (Journal of Philosophy 65(5):113–126, 1968; 68(7):203–211, 1971) ban on there (...) being multiple intra-world counterparts. I argue here that serious problems for ‘cheap haecceitism’ lurk very close to its surface, and they emerge when we consider the effect of using an actuality operator in our language. Among the most serious of the problems is the result that being the case in some possible world does not always suffice for possibly being the case. The result applies to any counterpart theory that employs a purely qualitative counterpart relation. The upshot is that if we are to admit haecceitist possibilities, as we should, then we must reject any purely qualitative relation as the one involved in the analysis of what might have been for an individual. (shrink)

From García-Carpintero and Kölbel, eds, Relative Truth.

It follows from Humean principles of plenitude, I argue, that island universes are possible: physical reality might have 'absolutely isolated' parts. This makes trouble for Lewis's modal realism; but the realist has a way out. First, accept absolute actuality, which is defensible, I argue, on independent grounds. Second, revise the standard analysis of modality: modal operators are 'plural', not 'individual', quantifiers over possible worlds. This solves the problem of island universes and confers three additional benefits: an 'unqualified' principle of compossibility (...) can be accepted; the possibility of nothing can be accommodated; and the identity of indiscernible worlds can be decisively refuted. (shrink)

In this chapter, I survey what I call Lewisian approaches to modality: approaches that analyze modality in terms of concrete possible worlds and their parts. I take the following four theses to be characteristic of Lewisian approaches to modality. (1) There is no primitive modality. (2) There exists a plurality of concrete possible worlds. (3) Actuality is an indexical concept. (4) Modality de re is to be analyzed in terms of counterparts, not transworld identity. After an introductory section in which (...) I motivate analyzing modality in terms of possible worlds, I devote one section to each of these four theses. For each thesis, I take Lewis’s interpretation and defense as my starting point. I then consider and endorse alternative ways of accepting the thesis, some of which disagree substantially with Lewis’s interpretation or defense. There is more than one way to be a Lewisian about modality. (shrink)

We argue that Anselm’s ontological argument (or at least one reconstruction of it) is based on an empirical version of Berry’s paradox. It is invalid, but it takes some understanding of trivalence to see why this is so. Under our analysis, Anselm’s use of the notion of existence is not the heart of the matter; rather, trivalence is.

Reliabilism about epistemic justification - the thesis that what makes a belief epistemically justified is that it was produced by a reliable process of belief-formation - must face two problems. First, what has been called "the new evil demon problem", which arises from the idea that the beliefs of victims of an evil demon are as justified as our own beliefs, although they are not - the objector claims - reliably produced. And second, the problem of diagnosing why skepticism is (...) so appealing despite being false. I present a special version of reliabilism, "indexical reliabilism", based on two-dimensional semantics, and show how it can solve both problems. (shrink)

Actualists routinely characterize their view by means of the slogan, “Everything is actual.” They say that there aren’t any things that exist but do not actually exist—there aren’t any “mere possibilia.” If there are any things that deserve the label ‘possible world’, they are just actually existing entities of some kind—maximally consistent sets of sentences, or maximal uninstantiated properties, or maximal possible states of affairs, or something along those lines. Possibilists, in contrast, do think that there are mere possibilia, that (...) there are things that are not actual. They think that more exists than what actually exists. All I have done so far, though, is rephrase the slogan in various ways. To say that everything is actual is precisely to say that there are no things that do not actually exist, which is precisely to say that there are no mere possibilia, and which is also precisely to say that we cannot sep- arately quantify over what exists and what is actual. These claims all amount to the same thing. But what is that, exactly? What on earth does it mean to say that everything is actual, that there are no mere possibilia, and so on? What does the actualist slogan really come to? I think the literature is far from clear on this point, and that people work themselves into unnecessary muddles because of it. Indeed, certain confusions that I shall discuss in the first half of this article seem to be on the rise. It is high time to lay out the issues and the choice points as clearly as possible. There are two primary choices to be made; there are two axes along which versions of actualism can vary. One choice has to do with how to treat claims about things that merely could exist. The other choice has to do with the modal status of the view and of how we should think about the “actual” in actualism. I make no claim that the positions I will eventually endorse are star- tlingly new. I think that most people will agree with the decisions I make at both choice points and will in fact find some bits of this essay obvious. But not everyone agrees with my decisions, and it has been my experience that people differ remarkably about which bits they find obvious—a fact I find rather telling. My goal, then, is to show that the two axes are there and to clarify the consequences of the choices. (shrink)

This paper presents a new theory of the truth conditions for indicative conditionals. The theory allows us to give a fairly unified account of the semantics for indicative and subjunctive conditionals, though there remains a distinction between the two classes. Put simply, the idea behind the theory is that the distinction between the indicative and the subjunctive parallels the distinction between the necessary and the a priori. Since that distinction is best understood formally using the resources of two-dimensional modal logic, (...) those resources will be brought to bear on the logic of conditionals. (shrink)

The paper deals with the problem of axiomatizing a system T1 of discrete tense logic, where one thinks of time as the set Z of all the integers together with the operations +1 ("immediate successor") and-1 ("immediate predecessor"). T1 is like the Segerberg-Sundholm system WI in working with so-called infinitary inference ruldes; on the other hand, it differs from W I with respect to (i) proof-theoretical setting, (ii) presence of past tense operators and a "now" operator, and, most importantly, with (...) respect to (iii) the presence in T1 of so-called systematic frame constants, which are meant to hold at exactly one point in a temporal structure and to enable us to express the irreflexivity of such structures. Those frame constants will be seen to play a paramount role in our axiomatization of T1. (shrink)

This paper argues in favor of a treatment of discourse about fiction in terms of operators on character, that is, Kaplanesque ‘monsters’. The first three sections criticize the traditional analysis of ‘according to the fiction’ as an intensional operator, and the approach to fictional discourse grounded on the notion of contextual shifts. The final sections explain how an analysis in terms of monsters yields the correct readings for a variety of examples involving modal and temporal indexicals.

In this paper, the authors show that there is a reading of St. Anselm's ontological argument in Proslogium II that is logically valid (the premises entail the conclusion). This reading takes Anselm's use of the definite description "that than which nothing greater can be conceived" seriously. Consider a first-order language and logic in which definite descriptions are genuine terms, and in which the quantified sentence "there is an x such that..." does not imply "x exists". Then, using an ordinary logic (...) of descriptions and a connected greater-than relation, God's existence logically follows from the claims: (a) there is a conceivable thing than which nothing greater is conceivable, and (b) if <em>x</em> doesn't exist, something greater than x can be conceived. To deny the conclusion, one must deny one of the premises. However, the argument involves no modal inferences and, interestingly, Descartes' ontological argument can be derived from it. (shrink)

In this discussion of Colin McGinn's book, 'Logical Properties', I comment first on the chapter "Existence", then on the chapter "Modality." With respect to existence, I argue that McGinn's view that existence is a property that some objects have and other objects lack requires the property of existence to be fundamentally unlike ordinary qualitative properties. Moreover, it opens up a challenging skeptical problem: how do I know that I exist? With respect to modality, I argue that McGinn's argument that quantificational (...) analyses of modality in terms of possible worlds are inevitably circular does not apply to modal theorists who hold that the notion of an impossible world is incoherent. (shrink)

According to David Lewis, a realist about possible worlds must hold that actuality is relative: the worlds are ontologically all on a par; the actual and the merely possible differ, not absolutely, but in how they relate to us. Call this 'Lewisian realism'. The alternative, 'Leibnizian realism', holds that actuality is an absolute property that marks a distinction in ontological status. Lewis presents two arguments against Leibnizian realism. First, he argues that the Leibnizian realist cannot account for the contingency of (...) actuality. Second, he argues that the Leibnizian realist cannot explain why skepticism about one's own actuality is absurd. In this paper, I mount a defense of Leibnizian realism. (shrink)

– The paper defends a naturalistic version of modal actualism according to which what is metaphysically possible is determined by dispositions found in the actual world. We argue that there is just one world—this one—and that all genuine possibilities are anchored by the dispositions exemplified in this world. This is the case regardless of whether or not those dispositions are manifested. As long as the possibility is one that would obtain were the relevant disposition manifested, it is a genuine possibility. (...) Furthermore, by starting from actual dispositional properties and branching out, we are able to include possibilities that are quite far removed from any state of affairs that happens to obtain, while still providing a natural and actual grounding of possibility. Stressing the importance of ontological considerations in any theory of possibility, it is argued that the account of possibility in terms of dispositional properties provides a more palatable ontology than those of its competitors. Coming at it from the other direction, the dispositional account of possibility also provides motivation for taking an ontology of dispositions more seriously. As well as the relevant dispositional notions required to lay out the view, the paper discusses the dispositional realism needed as the basis for the account of possibility. (shrink)

In his 2022 article ‘A puzzle about the fixity of the past’, Lampert argues that standard views concerning knowledge and the semantics of ‘actually’ conflict with a widely held principle concerning the fixity of the past. I show that his attempt to establish the conflict fails, as it rests on the implicit assumption that a past mental state or utterance involving a modal indexical must have the same content across worlds with a shared past, when in fact it must, given (...) its character, differ in content. (shrink)

در نگاه نخست به نظر می‌رسد می‌توان شباهت‌هایی بین جهان‌های ممکن مورد نظر لوئیس و نظریۀ جهان‌های موازی فیزیک یافت. هر دو این نظریات به امکان وجود جهان‌هایی بیش از جهانی که در آن زندگی می‌کنیم، اشاره دارند. پس از رسالۀ اورت، توجه فیزیک‌دانان به چندجهانی و جهان‌های موازی جلب شد. اکنون جهان‌های موازی یکی از نظریه‌های مورد توجه دانشمندان و پژوهشگران حوزۀ فیزیک است. دیوید لوئیس با تکیه بر فیزیکالیسم و رئالیسم موجهاتی از جمله طرفداران نظریۀ جهان‌های ممکن است. (...) در این مقاله کوشیده‌ایم با استفاده از روش تحلیلی-توصیفی ابتدا مبانی دو نظریه را تبیین کرده و سپس نظریۀ لوئیس را در مورد جهان‌های ممکن با توجه به نظریۀ جهان‌های موازی مورد بررسی قرار دهیم. هر دو نظریه وجود جهان‌های دیگر را ممکن می‌دانند. نظریه لوئیس شش ویژگی اصلی دارد: ۱- وجود و واقعیت جهان‌های ممکن، ۲- عدم وجود رابطه علی میان‌ جهان‌های ممکن، ۳- شباهت جهان‌های ممکن با جهان ما و تفاوت در محتوای جهان‌ها، ۴- عدم امکان تقلیل جهان‌های ممکن، ۵- نمایه‌ای بودن واقعیت و ۶- اتحاد مکان- زمان اجزای هر جهان و مجزا بودن روابط زمان-مکان جهان‌ها. نتایج پژوهش نشان می‌دهد در صورتی که جهان‌های موازی، زمانی به عنوان یک حقیقت علمی مورد تأیید قرار بگیرند، آنگاه ممکن است ویژگی‌های دوم، سوم و ششم نظریۀ لوئیس با واقعیت فیزیکی در تضاد قرار بگیرند. در صورت وجود تضاد -به جهت بنیادی بودن این ویژگی‌ها- نظریۀ جهان‌های ممکن لوئیس دچار تزلزل فراوان خواهد شد. (shrink)

The new evil demon problem amounts to a difficult challenge for the externalist about epistemic justification. Many solutions to the problem have been proffered in the almost 40 years since its first appearance in the literature. Among the more promising responses is indexical reliabilism, a combination of two versions of actual world reliabilism where “actual” denotes either the world of utterance or a rigidly determined actual world. This paper does three things. First, it attempts to clarify indexical reliabilism and how (...) it purports to solve the new evil demon problem. Second, it attempts to mitigate some of the prominent criticism that has been leveled against the theory. Third, it poses an explanatory challenge for the theory which remains even after all of the premises supporting indexical reliabilism are accepted. The conclusion is that indexical reliabilism is not tenable until a linguistic mechanism for the use of “actually reliable” has been offered that explains how the theory avoids collapsing into a two-concepts response to the new evil demon problem. (shrink)