Kristie Miller

We investigated, experimentally, the contention that the folk view, or naïve theory, of time, amongst the population we investigated is dynamical. We found that amongst that population, ~ 70% have an extant theory of time that is more similar to a dynamical than a non-dynamical theory, and ~ 70% of those who deploy a naïve theory of time deploy a naïve theory that is more similar to a dynamical than a non-dynamical theory. Interestingly, while we found stable results across our two experiments regarding the percentage of participants that have a dynamical or non-dynamical extant theory of time, we did not find such stability regarding which particular dynamical or non-dynamical theory of time they take to be most similar to our world. This suggests that there might be two extant theories in the population—a broadly dynamical one and a broadly non-dynamical one—but that those theories are sufficiently incomplete that participants do not stably choose the same dynamical theory as being most similar to our world. This suggests that while appeals to the ordinary view of time may do some work in the context of adjudicating disputes between dynamists and non-dynamists, they likely cannot do any such work adjudicating disputes between particular brands of dynamism.

It has widely been assumed, by philosophers, that our first-person preferences regarding pleasurable and painful experiences exhibit a bias toward the future (positive and negative hedonic future-bias), and that our preferences regarding non-hedonic events (both positive and negative) exhibit no such bias (non-hedonic time-neutrality). Further, it has been assumed that our third-person preferences are always time-neutral. Some have attempted to use these (presumed) differential patterns of future-bias—different across kinds of events and perspectives—to argue for the irrationality of hedonic future-bias. This paper experimentally tests these descriptive hypotheses. While as predicted we found first-person hedonic future-bias, we did not find that participants were time-neutral in all other conditions. Hence, the presumed asymmetry of hedonic/non-hedonic and first/third-person preferences cannot be used to argue for the irrationality of future-bias, since no such asymmetries exist. Instead, we develop a more fine-grained approach, according to which three factors—positive/negative valence, first/third-person, and hedonic/non-hedonic—each independently influence, but do not determine, whether an event is treated in a future-biased or time-neutral way. We discuss the upshots of these results for the debate over the rationality of future-bias.

That we find the idea of travelling in time, and in particular travelling backwards in time, fascinating, is evidenced by the plethora of new science fictions shows depicting time travel that hit our TV screens in 2016. I love time travel shows, and I can hardly keep up. In almost all cases these shows depict what philosophers call inconsistent time travel stories: stories that commit what my colleague Nick Smith (The University of Sydney) calls the second time around fallacy. These stories depict individuals travelling back in time (or in some cases sending a signal back in time) in order to change some past event (or, in some cases, to try and mitigate the changes brought about by some other time travellers). It’s easy to see why these storylines are captivating. They ask us to imaginatively entertain questions about the robustness of the present. We are asked to ponder to what extent the way things are now is the product of fluky events, so that had the past been ever so slightly different, the present would be very different indeed. These questions are intriguing because we all wonder to what extent our present selves are the result of choices we made, where we could so easily have made others, and to what extent who we are is most robust, resilient under small changes in our past decisions.

In a lot of domains in metaphysics the tacit assumption has been that whichever metaphysical principles turn out to be true, these will be necessarily true. Let us call necessitarianism about some domain the thesis that the right metaphysics of that domain is necessary. Necessitarianism has flourished. In the philosophy of maths we find it held that if mathematical objects exist, then they do of necessity. Mathematical Platonists affirm the necessary existence of mathematical objects (see for instance Hale and Wright 1992 and 1994; Wright 1983 and 1988; Schiffer 1996; Resnik 1997; Shapiro 1997 and Zalta 1988) while mathematical nominalists, usually in the form of fictionalists, hold that necessarily such objects fail to exist (see for instance Balaguer 1996 and 1998; Rosen 2001 and Yablo 2005). In metaphysics more generally, until recently it was more or less assumed that whatever the right account of composition—the account of under what conditions some xs compose a y—that account will be necessarily true (for a discussion of theories of composition see Simons 1987 and van Inwagen 1987 and 1990; the modal status of the composition relation is explicitly addressed in Schaffer 2007; Parsons 2006 and Cameron 2007). Similarly, it has generally been assumed that whatever the right account is of the nature of properties, whether they be universals, tropes, or whether nominalism is true, that account will be necessarily true (though see Rosen 2006 for a recent suggestion to the contrary). In considering theories of persistence it has been widely held that whether objects endure or perdure through time is a matter of necessity (Sider 2001; though see Lewis 1999 p227 who defends contingent perdurantism). And with respect to theories of time it is frequently held that whichever of the A- or B-theory is true is necessarily true. A-theorists often argue that there is time in a world only if the A-theory is true at that world (see for instance McTaggart 1903; Markosian 2004; Bigelow 1996; Craig 2001) while B-theorists often argue that the A-theory is internally inconsistent (Smart 1987; Mellor 1998; Savitt 2000 and Le Poidevin 1991). Once again, we find a few recent contingentist dissenters. Bourne (2006) suggests that it is a contingent feature of time that it is tensed, and thus that the A-theory is contingently true. Worlds in which there exist only B-theoretic properties are worlds with time, it is just that time in those worlds time is radically different to the way it is actually. Other defenders of the B-theory, though not expressly contingentists, do offer arguments against versions of the A-theory that try to show that such A-theories theories are inconsistent with the actual laws of nature (see for instance Saunders 2002 and Callender 2000); these arguments, at least, leave room for the possibility that the A-theories in question are contingently false (at least on the assumption that the laws of nature are themselves contingent, an assumption that not everyone accepts). Despite some notable exceptions, necessitarianism has flourished in many, if not most, domains in metaphysics. One such exception is Lewis’ famous defence of Humean supervenience as a contingent claim about our world. Lewis does not argue that necessarily, the supervenience base for all matters of fact in a world is nothing but a vast mosaic of local matters of particular fact. Rather, he thinks that we have reason to think that our world is one in which Humean supervenience holds (see Lewis 1986 p9-10 and 1994). Another exception to the necessitarian orthodoxy is to be found in the lively debate about the modal status of the laws of nature. Here, if anything, contingentism has been the dominating force, with it generally being held that there are possible worlds in which different laws of nature hold (this view is defended by, among others, Lewis 1986 and 2010; Schaffer 2005 and Sidelle 2002). Necessitarian dissenters hold that the laws of nature are necessary, frequently because they think it is necessary that fundamental properties have the causal or nomic profiles they do (see for instance Shoemaker 1980 and 1988; Swoyer 1982; Bird 1995; Ellis and Lierse 1994). Nevertheless, when it comes to thinking about the nature of the laws themselves, the necessitarian presumption is back on firm footing. Though there is disagreement about whether the laws are generalisations that feature in the most virtuous true axiomatisation of all the particular matters of fact (often known as the Humean view of laws and defended by Ramsey 1978; Lewis 1986 and Beebee 2000) or whether laws are relations of necessity that hold between universals (a view defended by Armstrong 1983; Dretske 1977; Tooley 1977 and Carroll 1990) no one has seriously suggested that it might be a contingent matter which of these is the right account of laws. The necessitarian orthodoxy is not surprising since metaphysics is largely an a priori process. While a priori reasoning may be used to determine whether a proposition is necessary or contingent, it is not well placed (in the absence of a posteriori evidence) to determine whether a contingent proposition is actually true or false. Since metaphysicians aim to tell us which principles are true in which worlds, on the face of it the discovery that metaphysical principles are contingent seems to make part of the task of metaphysics epistemically intractable. In what follows I consider two reasons one might end up embracing contingentism and whether this would lead one into epistemic difficulty. The following section considers a route to contingent metaphysical truths that proceeds via a combination of conceptual necessities and empirical discoveries. Section 3 considers whether there might be synthetic contingent metaphysical truths, and the final section raises the question of whether if there were such truths we would be well placed to come to know them.

ABSTRACT Temporal dynamists argue that we should believe that there exists temporal passage because there being passage is the best explanation for the presence of our temporal phenomenology. Presentists argue that presentism is the best version of temporal dynamism. Therefore, conditional on us accepting temporal dynamism, we should accept presentism. In this paper it is argued that if we understand temporal passage as the presentist does, such an argument can succeed only if dualism is true. Thus, we conclude, either presentists should embrace dualism, or they should reject any argument for presentism that proceeds via any such argument for temporal passage that proceeds via considerations of what best explains our temporal phenomenology.

There is considerable philosophical dispute about what it takes for an action to be evil. The methodological assumption underlying this dispute is that there is a single, shared folk conception of evil action deployed amongst culturally similar people. Empirical research we undertook suggests that this assumption is false. There exist, amongst the folk, numerous conceptions of evil action. Hence, we argue, philosophical research is most profitably spent in two endeavours. First, in determining which (if any) conception of evil action we have prudential or moral (or both) reason to deploy, and second, in determining whether we could feasibly come to adopt that conception as the single shared conception given our psychological make-up and the content of the conceptions currently deployed.

Time is woven into the fabric of our lives. Everything we do, we do in and across time. It is not just that our lives are stretched out in time, from the moment of birth to the moment of our death. It is that our lives are stories. We make sense of ourselves, today, by understanding who we were yesterday, and the day before, and the day before that; by understanding what we did and why we did it. Our memories shape our present selves, since we are the product of who we were, and who we remember being. Yet who we are lasts for but a moment. It is who we will be that demands attention. We are forever projecting ourselves into the future. We painstakingly plan for the needs of our future selves, all the while knowing that while what we do will make those future selves who they are, still, our future selves are elusive. So it is not simply that we happen to live our lives in time, the way, say, one might happen to live in Australia, or Singapore. It is hard to fathom how things could be otherwise. What would it be to live a life without time? Yet time itself is intangible. Though we are keenly aware of what has been ‒ of pain and loss, regret and pride ‒ and of what might be ‒ of anticipation, and dread, and longing ‒ time itself seems unaffected by anything we do. Though we can anticipate a future birthday cake, time itself cannot be tasted. Though we can dread a future dentist’s appointment, time itself cannot be touched. Though we remember the crunching of leaves this past autumn, time itself cannot be heard. How can it be that something so central to each of us, to who we are, and what we care about, can be so spectral? What, in the end, is time? Is time real, like a substance in which each of us, like insects in amber, finds ourselves trapped? Is time a dimension through which we can move? Is time not a thing at all, but some connection between events? If time is real, what is it like? Does it flow like a river, taking each of us prisoner in its current, washing us ever closer to the end of our lives? Is time like a cresting wave, coming ever closer to each of us from the future, engulfing us, and then receding into the past? Or is time static? Like a one-way road that each of us might wander, with no chance to turn back? Or perhaps time is like none of these things. Perhaps time is more like space; something we can navigate freely, so that we can visit different times just like we visit different places. Perhaps we can we travel in time the way we can travel in space. These questions, and many more, are the focus of this book. Now, you might wonder what philosophers are doing writing a book about time. Surely that’s a job for physicists! It is true: a great deal of what we know about time stems from our understanding of physics. However, even in physics we find that there are questions about time that go unanswered. Moreover, increasingly, physicists are turning to philosophers for help in understanding the role that time plays in current physical theories. Our goal is to get the reader up to speed on some of the central issues that influence our understanding of time so that they too may play a role in this ongoing discussion between science and philosophy. We hope that in doing so it will become clear what philosophy can bring to the study of time. There is a natural narrative in philosophy regarding the study of time, and we have chosen to organise this book according to that narrative. However, the book may also be approached in a ‘choose-your-own adventure’ spirit. While later chapters build on material introduced in earlier chapters, you can skip around, reading the book in any order you choose. For the instructor, this means that she can design her course around this book in any number of ways, depending on the particular topic she wishes to focus on.

This paper defends Flatland—the view that there exist neither determination nor dependence relations, and that everything is therefore fundamental—from the objection from explanatory inefficacy. According to that objection, Flatland is unattractive because it is unable to explain either the appearance as of there being determination relations, or the appearance as of there being dependence relations. We show how the Flatlander can meet the first challenge by offering four strategies—reducing, eliminating, untangling and omnizing—which, jointly, explain the appearance as of there being determination relations where no such relations obtain. Since, plausibly, dependence relations just are asymmetric determination relations, we argue that once we come mistakenly to believe that there exist determination relations, the existence of other asymmetries (conceptual and temporal) explains why it appears that there are dependence relations.

The A-theory and the B-theory advance competing claims about how time is grounded. The A-theory says that A-facts are more fundamental in grounding time than are B-facts, and the B-theory says the reverse. We argue that whichever theory is true of the actual world is also true of all possible worlds containing time. We do this by arguing that time is uniquely groundable: however time is actually grounded, it is necessarily grounded in that way. It follows that if either the A-theory or the B-theory is actually false, then it is necessarily false.

In this paper I develop a version of universalism that is non-mereological. Broadly speaking, non-mereological universalism is the thesis that for any arbitrary set of objects and times, there is a persisting object which, at each of those times, will be constituted by those of the objects that exist at that time. I consider two general versions of non-mereological universalism, one which takes basic simples to be enduring objects, and the other which takes simples to be instantaneous objects. This yields three versions of endurantism, of which I ultimately defend the version I call universalist endurantism. Universalist endurantism is the thesis that for any arbitrary set S of instantaneous simples that exist at the same instant, there exists a fusion of the members of S, and for any arbitrary set S* of instantaneous fusions each of which exist at a different instant, there exists an enduring object O that is constituted by those fusions at those instants. Universalist endurantism is ‘non-mereological’ in that the relation that holds between instantaneous fusions and persisting objects is not the part/whole relation, but rather, is the relation of constitution, thus allowing that the persisting objects are three rather than four dimensional. I argue that universalist endurantism not only has the various benefits of mereological universalism in allowing vagueness to be explicated as semantic indeterminacy, but in addition allows the endurantist to hold that some properties are genuinely intrinsic and are exemplified simpliciter.

Metaphysics is supposed to tell us about the metaphysical nature of our world: under what conditions composition occurs; how objects persist through time; whether properties are universals or tropes. It is near orthodoxy that whichever of these sorts of metaphysical claims is true is necessarily true. This paper looks at the debate between that orthodox view and a recently emerging view that claims like these are contingent, by focusing on the metaphysical debate between monists and pluralists about concrete particulars. This paper argues that we should be contingentists about monism and pluralism, and it defends contingentism against some necessitarian objections by offering an epistemology of contingent metaphysical claims.

Persons care about their future selves. They reason about their future selves’ interests; they plan for their future selves’ happiness and they worry about their future selves’ suffering. This paper is interested in the interplay between diachronic prudential reason and certain accounts of the metaphysics of personal identity that fall under the broad umbrella ‘conventionalist’. Some conventionalists conclude that under certain conditions there are intractable decisions for there is no fact of the matter regarding whether a person-stage ought (prudentially) to ϕ. This paper will suggest otherwise. These decisions are not intractable if we allow that it is sometimes rational for a person-stage to discount the utility of certain future person-stages. The paper then goes on to explore an alternative position that conventionalists might occupy which does not involve any such discounting: prudential relativism. According to prudential relativism it is impossible to offer a single, correct, answer to the question: should person-stage, P, ϕ at t? For according to prudential relativism there is no stage-independent stance from which to evaluate whether a person-stage ought to ϕ. Yet it is not, for all that, intractable, from P’s perspective, whether or not to ϕ.

One argument for the moving spotlight theory is that it better explains certain aspects of our temporal phenomenology than does any static theory of time. Call this the argument from passage phenomenology. In this paper it is argued that insofar as moving spotlight theorists take this to be a sound argument they ought embrace a new version of the moving spotlight theory according to which the moving spotlight is a cresting wave of causal efficacy. On this view it is more than just presentness that is temporary: a range of other fundamental properties are also temporary because presentness synchronically changes the fundamental properties that are instantiated in the present moment, from those instantiated when that moment is future, or past. On this view having experiences as of presentness co-varies with the presence of presentness, allowing the moving spotlight theorist to provide a compelling explanation for why we have the temporal phenomenology we do, and to explain how we can know that we are present by reflecting on the nature of said phenomenology.

A number of recent theories of quantum gravity lack a one-dimensional structure of ordered temporal instants. Instead, according to many of these views, our world is either best represented as a single three-dimensional object, or as a configuration space composed of such three-dimensional objects, none of which bear temporal relations to one another. Such theories will be empirically self-refuting unless they can accommodate the existence of conscious beings capable of representation. For if representation itself is impossible in a timeless world, then no being in such a world could entertain the thought that a timeless theory is true, let alone believe such a theory or rationally believe it. This paper investigates the options for understanding representation in a three-dimensional, timeless, world. Ultimately it concludes that the only viable option is one according to which representation is taken to be deeply non-naturalistic. Ironically then we are left with two seemingly very unattractive options. Either a very naturalistic motivation—taking seriously a live view in fundamental physics—leads us to a very non-naturalistic view of the mental, or else views in the philosophy of mind partly dictate what is an acceptable theory in physics.

Temporal non-dynamists hold that there is no temporal passage, but concede that many of us judge that it seems as though time passes. Phenomenal Illusionists suppose that things do seem this way, even though things are not this way. They attempt to explain how it is that we are subject to a pervasive phenomenal illusion. More recently, Cognitive Error Theorists have argued that our experiences do not seem that way; rather, we are subject to an error that leads us mistakenly to believe that our experiences seem that way. Cognitive Error Theory is a relatively new view and little has been said to explain why we make such an error, or where, in the cognitive architecture, such an error might creep in. In this paper we remedy this by offering a number of hypotheses about the source of error. In so doing we aim to show that Cognitive Error Theory is a plausible competitor to Phenomenal Illusion Theory.

This paper argues for a particular view about in what metaphysical equivalence consists: namely, that any two metaphysical theories are metaphysically equivalent if and only if those theories are strongly hyperintensionally equivalent. It is consistent with this characterisation that said theories are weakly hyperintensionally distinct, thus affording us the resources to model the content of propositional attitudes directed towards metaphysically equivalent theories in such a way that non-ideal agents can bear different propositional attitudes towards metaphysically equivalent theories.

Ross Cameron's The Moving Spotlight argues that of the three most common dynamical theories of time – presentism, the growing block theory and the moving spotlight theory – his version of the MST is the best. This paper focuses on Cameron's response the epistemic objection. It considers two of Cameron's arguments: that a standard version of the MST can successfully resist the epistemic objection, and that Cameron's preferred version of the MST has an additional avenue open to it for resisting the objection, one that is consistent with an appealing account of truthmaking. I argue that neither argument succeeds....By SMST, I shall mean the view that there exists a static four-dimensional block of events such that if an event ever...

It was once held to be a virtue of the growing block theory that it combines temporal dynamism with a straightforward account of in virtue of what past-tensed propositions are true, and an explanation for why some future-tensed propositions are not true (assuming they are not). This put the growing block theory ahead of its principal dynamist rival: presentism. Recently, new growing block theorists have suggested that what makes true, past-tensed propositions, is not the same kind of thing as what makes true, present-tensed propositions. They have done so in an attempt to defuse a particular epistemic objection to their view. In this paper it is argued that the new growing block theorist faces a dilemma. The more unified a strategy is for responding to the epistemic objection, the more that strategy results in the new growing block model positing truthmakers that are similar to those posited by the presentist, which erodes the purported advantage of the growing block theory over presentism. On the other hand, versions of the new growing block theory that embrace disunified strategies are better able to differentiate themselves from presentism, but are unattractive because of their disunity.

Many think that sentences about what metaphysically explains what are true iff there exist grounding relations. This suggests that sceptics about grounding should be error theorists about metaphysical explanation. We think there is a better option: a theory of metaphysical explanation which offers truth conditions for claims about what metaphysically explains what that are not couched in terms of grounding relations, but are instead couched in terms of, inter alia, psychological facts. We do not argue that our account is superior to grounding-based accounts. Rather, we offer it to those already ill-disposed towards grounding.

It is widely thought that grounding is a hyperintensional phenomenon. Unfortunately, the term ‘hyperintensionality’ has been doing double-duty, picking out two distinct phenomena. This paper clears up this conceptual confusion. We call the two resulting notions hyperintensionalityGRND and hyperintensionalityTRAD. While it is clear that grounding is hyperintensionalGRND, the interesting question is whether it is hyperintensionalTRAD. We argue that given well-accepted constraints on the logical form of grounding, to wit, that grounding is irreflexive and asymmetric, grounding is hyperintensionalTRAD only if one endorses a sentential operator view of grounding. We argue that proponents of the sentential operator view will need to distinguish two importantly different kinds of hyperintensionalityTRAD—weak and strong—and we offer them a way to do so.

My present inclination is to say that both identity and relational analyses are intelligible hypotheses. I reject the identity analysis, looking rather to relations between different phases to secure the unity of a particular over time. But I do not think that the identity view can be rejected as illogical. If it is to be rejected, then I think it must be rejected for Occamist reasons. The different phases exist, and so do their relations. These phases so related, it seems, are sufficient to secure identity through time for all particulars. I suggest, then, that the identity view of identity through time is not illogical. The question is rather whether it is a postulation which is fruitful, or expedient, or which we are compelled, to make. (Armstrong p. 70, 1980) This paper considers this view, articulated by Armstrong and argues that recent work on persistence sheds light on this issue.

The book is divided into three parts. The first, containing three papers, focuses on the characterization of the central tenets of previii sentism (by Neil McKinnon) and eternalism (by Samuel Baron and Kristie Miller), and on the ‘sceptical stance’ (by Ulrich Meyer), a view to the effect that there is no substantial difference between presentism and eternalism. The second and main section of the book contains three pairs of papers that bring the main problems with presentism to the fore and outlines its defence strategy. Each pair of papers in this section can be read as a discussion between presentists and eternalists, wherein each directly responds to the arguments and objections offered by the other. This is a discussion that is sometimes absent in the literature, or which is at best carried out in a fragmented way. The first two papers of the section deal with the problem of the compatibility of Special Relativity Theory (SRT) and presentism. SRT is often considered to be a theory that contradicts the main tenet of presentism, thereby rendering presentism at odds with one of our most solid scientific theories. Christian Wüthrich’s paper presents arguments for the incompatibility of the two theories (SRT and presentism) within a new framework that includes a discussion of further complications arising from the theory of Qauantum Mechanics. Jonathan Lowe’s paper, by contrast, develops new general arguments against the incompatibility thesis and replies to Wüthrich’s paper. The second pair of papers focuses on the problem that presentists face, in providing grounds for past tensed truths. In the first (by Matthew Davidson), new arguments are provided to defend the idea that the presentist cannot adequately explain how what is now true about the past is grounded, since for the presentist the past is completely devoid of ontological ground. The second paper (by Brian Kierland) takes up the challenge of developing a presentist explanation of past truths, beginning by outlining some existing views in the literature before advancing an original proposal.

This paper presents the strongest version of a non-perdurantist four-dimensionalism: a theory according to which persisting objects are four-dimensionally extended in space-time, but not in virtue of having maximal temporal parts. The aims of considering such a view are twofold. First, to evaluate whether such an account could provide a plausible middle ground between the two main competitor accounts of persistence: three-dimensionalism and perdurantist four-dimensionalism. Second, to see what light such a theory sheds on the debate between these two competitor theories. I conclude that despite prima facie reasons to suppose that non-perdurantist four-dimensionalism might be a credible alternative to either other account of persistence, ultimately the view is unsuccessful. The reasons for its failure illuminate the sometimes stagnant debate between three-dimensionalists and perdurantists, providing new reasons to prefer a perdurantist metaphysics.

Temporal dynamists argue that we should believe that there exists temporal passage because there being passage is the best explanation for the presence of our temporal phenomenology. Some non-dynamists have countered that the presence of passage makes no difference to our temporal phenomenology, and consequently that temporal phenomenology cannot be evidence that there is passage. This paper attempts to bolster this non-dynamist response by offering new arguments for the claim that the presence of passage makes no difference to our phenomenology.

This paper defends a view that falls somewhere between the two extremes of inflationary and deflationary accounts, and it does so by rejecting the initial conceptualisation of holes in terms of absences. Once we move away from this conception, I argue, we can see that there are no special metaphysical problems associated with holes. Rather, whatever one’s preferred metaphysics of paradigm material objects, that account can equally be applied to holes. This means that like the deflationist, I am entity monist: I reject the idea that there are any immaterial beings. On the other hand, like the inflationist I reject the idea that we should identify holes with parts or surfaces of paradigm objects. Like the inflationist, I hold that there exist entities in roughly the regions of space-time where pre-theoretically we would say there exist holes, and those entities are holes. Call this latter part of the view—that where the folk are apt to claim there is a hole, that hole has roughly the dimensions that the folk attribute to it—hole-instinctivism (the view that our instincts about hole location/dimension are roughly right). Ultimately I embrace hole conventionalism, a view that includes commitment to both entity monism and hole-instinctivism. According to hole conventionalism, holes are no more ontologically problematic than statues, nor are they of a fundamentally different ontological kind from statues.

In this paper, I argue that the thesis that time travel is logically possible, is inconsistent with the necessary truth of any of the usual ‘open futureobjective present’ models of the universe. It has been relatively uncontroversial until recently to hold that presentism is inconsistent with the possibility of time travel. I argue that recent arguments to the contrary do not show that presentism is consistent with time travel. Moreover, the necessary truth of other open future-objective present models which we might, prima facie, have supposed to be more amenable to the possibility of time travel, turn out also to be inconsistent with this possibility.

Conventionalism’ about personal-identity is an umbrella term for a cluster of views. All these views accept the core idea that conventions, or what are often known as person-directed practices, are crucially involved in the identity of persons over time, and that had those conventions or practices been different, the individuation and persistence conditions of persons would have been different.The purpose of this paper is not to argue for conventionalism broadly understood, nor for any particular version of conventionalism. That is a task I, and others have undertaken elsewhere. Rather, since there is frequent confusion about conventionalism, I will first be concerned to clarify what it is that conventionalists really say about the identity of persons over time. Since there are a number of different views that broadly fall under the banner of conventionalism, it will be part of the task of this paper to disentangle these views and determine what they have in common and where they disagree.