Daniel Nolan

A lot of philosophers engage in debates about what claims are “metaphysically necessary”, and a lot more assume with little argument that some classes of claims have the status of “metaphysical necessity”. I think we can usefully replace questions about metaphysical necessity with five other questions which each capture some of what people may have had in mind when talking about metaphysical necessity. This paper explains these five other questions, and then discusses the question “how much of metaphysics is metaphysically necessary?”, and each of its five replacements

It is almost universally believed that some infinite regresses are vicious, and also almost universally believed that some are benign. In this paper I argue that regresses can be vicious for several different sorts of reasons. Furthermore, I claim that some intuitively vicious regresses do not suffer from any of the particular aetiologies that guarantee viciousness to regresses, but are nevertheless so on the basis of considerations of parsimony. The difference between some apparently benign and some apparently vicious regresses, then, turns out to be a matter of a more general assessment of costs and benefits, making viciousness of regresses in some cases less of a local matter than is usually thought

Questions about necessity (or what has to be, or what cannot be otherwise) and possibility (or what can be, or what could be otherwise) are questions about modality. Fictionalism is an approach to theoretical matters in a given area which treats the claims in that area as being in some sense analogous to fictional claims: claims we do not literally accept at face value, but which we nevertheless think serve some useful function. However, despite its name, “Modal Fictionalism” in its usual manifestations is not primarily fictionalism about claims of necessity and possibility, but rather a fictionalist approach to claims about possible worlds. (For instance, modal fictionalism is not normally fictionalist about the claim that “it is possible that there be a species of tail-less kangaroo”, but rather about the claim that “there is a possible world in which there is a species of tail-less kangaroo”.) The practice of taking possible worlds to be merely convenient fictions, or of treating talk about possible worlds as being useful without being literally correct, is quite common in philosophical circles. It is only recently, however, that philosophers have seriously examined the implications of taking possible worlds to be merely fictional objects, like Sherlock Holmes or a frictionless surface.

The philosophy of necessity and possibility has flourished in the last half-century, but much less attention has been paid to the question of how we know what can be the case and what must be the case. Many friends of modal metaphysics and many enemies of modal metaphysics have agreed that while empirical discoveries can tell us what is the case, they cannot shed much light on what must be the case or on what non-actual possibilities there are. In this paper, in contrast, I discuss and defend naturalistic approaches to discovering the facts about necessity and possibility. After some remarks about what methodological naturalism in philosophy might amount to, I argue that naturalistic method in modal investigations may not need to be particularly revisionary of much of what is currently being done in modal investigation. I then discuss a number of respects in which a naturalistic orientation in modal investigation may improve on our current epistemic situation.

Bob Hale in Hale 1995b posed a dilemma for modal fictionalism (more specifically, Rosen's version of modal fictionalism). A modal fictionalist who maintains the version outlined in Rosen 1990 believes that the fiction of possible worlds (PW, to use Rosen and Hale's abbreviation) is not literally true. The question arises, however, about its modal status. Is it necessarily false, or contingently false? In either case, Hale argues, the modal fictionalist is in trouble. Should the modal fictionalist claim that the story of possible worlds is necessarily false, then the modal fictionalist cannot gloss their "according to the fiction of possible worlds ... ." prefix as "were the fiction of possible worlds true, then ... would be true". This is because, according to Hale, conditional claims with antecedents which are necessarily false are automatically true, so it follows that if the fiction of possible worlds is taken to be necessarily false, all conditionals of the form "were the fiction of possible worlds true then ..." are true, and not merely the ones that the modal fictionalist wishes to endorse. If the modal fiction is to be useful, not everything should be true according to it: examples of claims that had better not be true according to it include the claim that 2+2=7, or the claim that there are no possible worlds. On the other hand, if the fiction of possible worlds (PW) is only contingently false, Hale claims this also lands the Rosen's fictionalism in unacceptable trouble, though it is not so clear why (see below). Let me discuss these horns in turn.

Possible worlds have found many applications in contemporary philosophy: from theories of possibility and necessity, to accounts of conditionals, to theories of mental and linguistic content, to understanding supervenience relationships, to theories of properties and propositions, among many other applications. Almost as soon as possible worlds started to be used in formal theories in logic, philosophy of language, philosophy of mind, metaphysics, and elsewhere, theorists started to wonder whether impossible worlds should be postulated as well. In many applications, possible worlds face limitations that can be dealt with through postulating impossible worlds as well. This chapter examines some of the uses of impossible worlds, and philosophical challenges theories of impossible worlds face.

The question of the function of modal judgement is an interesting philosophical issue, and John Divers's paper (this volume) has persuaded me that it has not received the attention it deserves. I think it is an important and interesting question even apart from any more ambitious claims that are made about its role in settling other issues about modality. Even if we became convinced that the story about function put no constraints whatsoever, epistemologically or metaphysically, on a theory of modality, it would still remain an interesting question about one of the pervasive and perhaps fundamental things we do in our cognitive lives.

Modal Fictionalism, the theory that possible worlds do not literally exist but that our talk about them should be understood in the same way that we understand talk about fictional entities, is an increasingly popular approach to possible worlds. This paper will distinguish three versions of Modal Fictionalism, and will show that the third, a version endorsed by some of the most prominent Modal Fictionalists, faces at least three serious objections: that it makes modality too artificial, the modal fiction does not have the representative resources it needs, and the approach has trouble accounting for propositions.

To what extent do true predications correspond to truthmakers in virtue of which those predications are true? One sort of predicate which is often thought to not be susceptible to an ontological treatment is a predicate for instantiation, or some corresponding predication (trope-similarity or set-membership, for example). This paper discusses this question, and argues that an "ontological" approach is possible here too: where this ontological approach goes beyond merely finding a truthmaker for claims about instantiation. Along the way a version of the problem of the regress of instantiation is posed and solved.

A number of theories of dispositions to date have presupposed that dispositions are all causal:  when X is disposed to PHI in circumstances C, it is because of a potential causal connection between C and X’s PHIing. Other intimate connections between dispositions and causation have been argued for: that the relation between dispositions and their categorical bases is to be understood in causal terms, for example, or even that we can explain causation in dispositional terms. These theories of dispositions are all threatened by previously underappreciated cases of noncausal dispositions: cases where an X is disposed to PHI in C, but not because of potential causal connections between the manifestation conditions of dispositions and the manifestations themselves. This paper argues that there are noncausal dispositions of a number of different varieties, explains what trouble this causes many standard theories of dispositions, and discusses what lessons can be learned from these cases for the nature of dispositions. Some of the cases discussed will also cast doubt on the idea that all dispositions ground truths about potentiality or possibility.

A standing challenge in the theory of counterfactuals is to solve the “deviation problem”.  Consider ordinary counterfactuals involving an antecedent concerning a difference from the actual course of events at a particular time, and a consequent concerning, at least in part, what happens at a later time.  In the possible worlds framework, the problem is often put in terms of which are the relevant antecedent worlds. Desiderata for the solution include that the relevant antecedent worlds be governed by the actual laws of nature with no miracles; that the past in those worlds before the antecedent time matches the actual past; that the account is compatible with determinism, and that many of our ordinary counterfactual judgments are correct, and would be correct even given determinism. Many theorists have compromised on one or more of these desiderata, but this paper presents an account employing impossible worlds that satisfies them all.