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Cartesian modal arguments for property dualism presuppose that facts about the essential natures of pain and other qualitative properties can be grasped a priori by merely conceiving of them or imagining them. This chapter argues that this presupposition fails. It then proposes a theory of metaphysical necessity that in effect reduces it to the subjunctive conditional — to say that it is metaphysically necessary that p, it claims, is equivalent to saying that p would be the case no matter what else was the case. Using this theory of metaphysical necessity as a foundation, the chapter gives an account of how claims concerning metaphysical necessity can be known to be true. This account allows that such claims can, in many cases, be known a priori, but it implies that in many other cases, our grasp of them is a posteriori. The account sustains the criticisms of Cartesian modal arguments offered in the early sections of the chapter.

This chapter is mainly devoted to the conceivability argument against materialism, viewed through the lens of the two-dimensional semantic framework. The key issue is whether conceivability entails metaphysical possibility. The key opponent is the type-B materialist, who denies the entailment. Many objections and putative counterexamples to the conceivability-possibility thesis have been mooted: the chapter discusses fifteen or so putative counterexamples, along with ten or so objections of other sorts to the conceivability argument. It also sketches a positive grounding for the sort of modal rationalism that drives the conceivability argument.

Modal intuitions are not only the primary source of modal knowledge but also the primary source of modal error. An explanation of how modal error arises — and, in particular, how erroneous modal intuitions arise — is an essential part of a comprehensive theory of knowledge and evidence. This chapter begins with a summary of certain preliminaries: the phenomenology of intuitions, their fallibility, the nature of concept-understanding and its relationship to the reliability of intuitions, and so forth. It then identifies two sources of modal error: the first has to do with the failure to distinguish between metaphysical possibility and various kinds of epistemic possibility; the second, with the local misunderstanding of one's concepts (as opposed to out-and-out misunderstanding, as in Burge's original arthritis case). The first source of error is widely misunderstood; the second source has not been discussed in philosophical literature. This source of modal error, and the potential to overcome it, has wide-ranging implications for philosophical method. The failure to understand these sources of modal error has recently led to sceptical accounts of intuition and modal error, which are, ultimately self-defeating.

The “conceivability argument” for dualism is presented and analyzed in depth. It is argued that in order to derive the possibility of zombies – creatures physically like us but without conscious experience – from their conceivability, certain unwarranted semantic and epistemic doctrines must be accepted. By introducing the idea of a nonascriptive mode of presentation, it is argued that a materialist can consistently allow the conceivability of zombies without admitting their metaphysical possibility.

The defense of the regularity theory enables a conception of free will that incorporates counterfactual power. For the nomic impossibility of deciding otherwise does not preclude its metaphysical possibility. There are metaphysically possible worlds in which human agents violate the laws of the actual world. Moreover, through their capacity as decision makers, human agents in a deterministic world sometimes actually possess the power to violate the laws concerning their own decisions. Were one to violate the laws, the world would no longer be deterministic. This power to violate the laws of the actual world is a consequence of our nature as decision makers. Unlike the incompatibilist, who has to hope that the world has an indeterministic structure, the compatibilist believes that freedom is inherent in human agency. When added to DR-autonomy, counterfactual power becomes self-control or full free will.

This chapter discusses Saul Kripke’s treatment of the necessary a posteriori and concomitant distinction between epistemic and metaphysical possibility. It extracts the enduring lessons of his treatment of these matters and disentangles them from errors and confusions that mar some of his most important discussions. It argues that there are two Kripkean routes to the necessary a posteriori—one correct and philosophically far-reaching; the other incorrect, philosophically misleading, and the source of damaging errors that persist to this day. It connects two false principles involved in the second, unsuccessful, route to the necessary a posteriori with the plausible and potentially correct idea that believing a singular proposition that o is F always involves also believing a richer more descriptively informative proposition in which some further property plays a role in the agent’s thoughts about o. It explains why this idea will not save the failed second route to the necessary a posteriori and suggests that it may help reconcile Kripke’s insights with the lessons of Frege’s puzzle.

Many sentences represent the kind of world we inhabit, in the sense of providing putative information about it. For each such sentence, there is a set of possibilities, ways things might be, which are in accord with how things are being represented to be by the sentence, and which are such that the credence we give the sentence's being true is the sum of the credences we give to each of the possibilities being actual. Some say that, in fleshing out this attractive picture, we have to draw on the distinction between what's metaphysically possible and what's conceptually possible. This chapter argues that this is a mistake.

This chapter develops a moderate modal rationalism. According to this moderate modal rationalism, knowledge of metaphysical possibility and necessity is available through sensitivity to the rational entailment relations between propositions. The imagination can be used to explore these rational entailment relations so as to discover whether a proposition is “conceivable” in the sense that it does not rationally entail a rational absurdity. Some metaphysically impossible propositions are conceivable in this way, but their metaphysical impossibility can be discovered nonetheless by noticing that they rationally entail some proposition about the actual world that is, in fact, false.

This chapter develops a theory of rational modality—including rational entailment, possibility, necessity, and impossibility—to complement the theory of Fregean sense. Fregean senses are distinguished from one another by the rational (otherwise called “conceptual” or “epistemic”) possibilities in which they are true, where some of these possibilities are metaphysically impossible. It is suggested that one way to interpret “analytic” necessities and entailments is as rational necessities and entailments. Rational modality is motivated by the rationality version of Frege's puzzle; it can be rational to have a Hesperus mental representation—e.g. Hesperus is visible—without it being rational to have the corresponding Phosphorus mental representation—e.g. Phosphorus is visible—even though Hesperus is Phosphorus. This appearance can easily be accounted for if the concept Hesperus applies in different rational possibilities than the concept Phosphorus does.

This chapter defends an account of metaphysical possibility which is based on the idea that there is a close connection between metaphysical possibility and the ‘just is’-operator. The discussion centers on two main results. First, it is shown that a limited class of ‘just is’-statements can be used to fix a truth-value for every sentence in a first-order modal language. (This is the Extension Theorem.) Second, it is shown that the truth-conditions of arbitrary sentences in a modal language can be specified using only the fragment of the language that does not contain modal operators. (This is the Reduction Theorem.) The chapter also contains an extend discussion of a rival account of metaphysical possibility, defended by David Lewis.

This chapter claims that the whole history of the world is a succession of events, which consist in the instantiation of properties in substances at times. It analyses the criteria for two substances, properties, or events being the same. It analyses the nature of metaphysical possibility (via analysing logical possibility), and analyses what it is for one event to supervene on another event. When properties, substances, and times are picked out by informative designators, what is logically possible is also metaphysically possible. The criteria for the identity of a substance depend on whether substances of its genus have thisness or are simply bundles of instantiated properties.

It is often maintained (i) that conceivability is a reliable test for possibility, and also (ii) that conceivability is our primary way of obtaining knowledge of modality. Challenging (i), the chapter maintains that it is in fact psychologically possible to conceive of almost anything, including contradictions. Accordingly, conceivability is a trustworthy guide test for possibility only if we compare its results with principles that are independently known to be necessary. It follows that (ii) must be wrong—we must have some way of recognizing necessity that is independent of conceivability. It is proposed that necessity is known to us by virtue of our acceptance of certain ‘conceptual truths’—specifically, propositions that implicitly define the concept of necessity. The chapter also criticizes the Cartesian modal argument, and the idea, put forward by the author in earlier work, that the metaphysical modalities can be defined in terms of the counterfactual conditional.

Relates the ideal types of strategies presented in earlier chapters to actual proposals in the literature. We begin with the geometric strategy of Harty Field, and claim that our version better reveals what is really going on than do his own claims about mathematically formulated theories always being conservative extensions of corresponding nominalistic theories. We also consider strategies using modal logic, as found in the works of Charles Chihara and Geoffrey Hellman, emphasizing that one must distinguish metaphysical necessity and possibility from logical necessity and possibility, and use all the resources of cross‐comparison provided by ordinary language, in order to make these strategies work. A potpourri of further strategies is briefly examined.

This chapter asks: if one wishes to endorse a direct realist view of perception, in which in a case of seeing, seen objects or their particular features are somehow parts of the experience one undergoes, what other doctrines must one endorse? Direct realists think that we can't get a clear view of the nature of hallucinating. There are many epistemic possibilities to be had from a single hallucination. But if there are many epistemic possibilities for a single hallucination then there are also metaphysical possibilities for the hallucination that subjectively match it.

What is metaphysics? And how is it to be pursued? Elsewhere, I have defended the view that the central task of metaphysics is to chart the possibilities of being: knowledge of what is actual presupposes knowledge of what is possible—of what is really or metaphysically possible. According to this conception of the aim and content of metaphysical theory, metaphysics is above all concerned with identifying the fundamental ontological categories to which all entities, actual and possible, belong. It is, therefore, incumbent upon metaphysicians to explain what it is that grounds metaphysical possibility. This chapter argues that the only coherent account of the ground of metaphysical possibility and of our capacity for modal knowledge is a version of essentialism: a version that I call serious essentialism, to distinguish it from views which appear very similar to it but which, in fact, differ from it fundamentally in certain crucial respects.

‘Constrict theories’ are those theories whereby a law of nature resolves the Grandfather Paradox. This chapter introduces two such positions: the Chronology Protection Conjecture (whereby the laws rule out time travel) and Novikov’s Principle of Self-Consistency (which says that time travel is possible but that the laws of nature will ensure that there are no paradoxes). This chapter argues that because the Grandfather Paradox is a thought experiment, and aims to conclude something about metaphysical possibility, these theories are irrelevant. The chapter ends by discussing whether we should reinterpret the Grandfather Paradox as arguing for time travel’s physical impossibility instead.

This chapter focuses on the nature of ontological categories. The author argues that, insofar as the notion of an ontological category is theoretically fruitful, we should take ontological categories to be modes of being. The chapter discusses one way in which ontological categories as modes of being could be used to formulate interesting and powerful principles about what is metaphysically possible. This way appeals to the idea that there are type restrictions in the metaphysically perfect language. The chapter also discusses whether it is necessary what ontological categories there are, and the prospects for a putative discipline of formal ontology, understood as that which studies the essence of an object qua object.

This chapter is divided into four parts, corresponding to the partitioning of the essays in the volume. Part I, on neo-Fregeanism in the philosophy of mathematics develops replies to Demopolous, Heck, Rosen and Yablo, Boolos and Edwards; Part II, on vagueness, intuitionistic logic and the Sorites Paradox develops replies to Rumfitt and Schiffer; Part III, on revisionism in the philosophy of logic develops replies to Shieh and Tennant; and Part IV, on the epistemology of metaphysical possibility develops a reply to Hale. In each section, Crispin Wright offers an overview of the relevant area and outlines and refines his views on the relevant topics. Inter alia, he offers detailed replies to each of the ten contributed essays in the volume.