Theodore Sider

‘Composition as identity’ is the radical claim that the whole is identical to the parts—radical because it implies that a single object can be identical to many objects. Composition as identity, together with auxiliary assumptions, implies the principle of ‘collapse’: an object is one of some things if and only it is part of the fusion of those things. Collapse has important implications: the comprehension principle of plural logic must be restricted, plural definite descriptions such as ‘the Cheerios in the bowl’ are empty, composition as identity does not preclude emergent properties (contrary to what McDaniel has argued), and drastic simplifications of mereological and logical ideology are extensionally available.

_In a series of thought-provoking and original essays, eighteen leading philosophers engage in head-to-head debates of nine of the most cutting edge topics in contemporary metaphysics._ Explores the fundamental questions in contemporary metaphysics in a series of eighteen original essays - 16 of which are newly commissioned for this volume Features an introductory essay by the editors on the nature of metaphysics to prepare the reader for ongoing discussions Offers readers the unique opportunity to observe leading philosophers engage in head-to-head debate on cutting-edge metaphysical topics Provides valuable insights into the flourishing field of contemporary metaphysics.

According to the best-system theory, a law of nature is nothing more than a certain kind of pattern in what actually happens. Out of all the possible "systems'' (sets of sentences), there is one that does a better job than all of the others in summarizing a lot of what actually happens in a simple way; the sentences in this best system, according to the best-system theory, are the laws of nature. David Lewis's version of this idea appealed to a distinction between natural and non-natural properties. But various people have objected that this opens up an epistemic gap between science and metaphysics, and have gone on to propose versions of the best-system theory that do not appeal to naturalness. I defend Lewis's version of the best-system theory against the objection, and discuss various problems confronting naturalness-free versions.

Four-Dimensionalism defends the thesis that the material world is composed of temporal as well as spatial parts. This defense includes a novel account of persistence over time, new arguments in favour of the four-dimensional ontology, and responses to the challenges four-dimensionalism faces. Theodore Sider pays particular attention to the philosophy of time, including a strong series of arguments against presentism, the thesis that only the present is real. Arguments offered in favour of four-dimensionalism include novel arguments based on time travel, the debate beween spacetime substantivalists and relationalists, and vagueness. Also included is a comprehensive discussion of the paradoxes of coinciding material objects, and a novel resolution of those paradoxes based on temporal counterpart theory. In conclusion Sider replies to prominent objections to four-dimensionalism, including discussion of the problem of the rotating homogenous disk.Four Dimensionalism is an original and highly readable study of the metaphysics of time and identity.

The questions of metaphysics are the deepest and most puzzling questions there are. What is time? Am I free in my actions? What makes me the same person I was as a child? What is it for one thing to cause another? Riddles of Existence is the first book ever to make metaphysics genuinely accessible and fun. Its lively, informal style brings the riddles to life and shows how stimulating it can be to think about them. No philosophical background is required to enjoy this book: anyone who has thought about life's most profound questions will find plenty to provoke and entertain them here.

According to the high-dimensional approach to quantum mechanics (a.k.a. wavefunction realism), the fundamental space of our world has an unfathomably large number of dimensions. This account is empirically adequate only if the three-dimensional manifest image can somehow be recovered from high-dimensional reality. A proper understanding of inter-level metaphysics (a.k.a. metaphysical explanation, grounding, etc.) shows that the manifest image can indeed be recovered, and answers the most concerning objections to high-dimensionalism. But it also shows that high-dimensionalism has disturbing consequences about the objectivity of the manifest image.

Quantifier variantists accept multiple alternative ontological languages in which quantifiers obey the usual inference rules despite having different meanings. But collapse arguments seem to show that these quantifiers would be provably equivalent to one another. Cian Dorr has pushed this discussion forward by formulating the collapse argument in terms of an algebra of meanings that are common amongst the languages. I attempt to show that quantifier variantists can respond. But an important distinction between types of quantifier variance emerges, between those in which quantifier meanings draw on a single objective backbone of “portions of reality,” and those (such as the type that is arguably associated with neo-Fregeanism) in which they do not.

In this chapter the author examines the idea of time's motion, or flow, more carefully, by comparing it to the motion of ordinary objects. Ordinary objects move with respect to time. So if time itself moves, it must move with respect to some other sort of time. But what would that other time be? Most motion takes place with respect to the familiar timeline, but time itself moves with respect to another timeline, hypertime. Hypertime is supposed to be a sort of time. Hypertime must move with respect to yet another sort of time, hyper‐hyper time. Space‐time diagrams can be used to represent all of history; everything that has ever happened or ever will happen can be fit into a space‐ time diagram somewhere. According to the space‐time theory, time and space are analogous in many ways. Finally the author argues against the space‐time theory.

Nonreductive materialism is the dominant position in the philosophy of mind. The global supervenience of the mental on the physical has been thought by some to capture the central idea of nonreductive materialism: that mental properties are ultimately dependent on, but irreducible to, physical properties. But Jaegwon Kim has argued that global psychophysical supervenience does not provide the materialist with the desired dependence of the mental on the physical, and in general that global supervenience is too weak to be an interesting dependence relation. We argue that these arguments are unsound. Along the way, we clarify the relationship between global and strong supervenience, and show clearly what sort of dependence global supervenience provides

Shamik Dasgupta has argued that realists about natural properties (and laws, grounding, etc.) cannot account for their epistemic value. For "properties are cheap": in addition to natural properties and any value the realist might attach to them, there are also "shmatural" properties (standing to natural properties like charge and mass as Goodman's grue and bleen stand to green and blue) and a corresponding "shmvalue" of theorizing in terms of them. Dasgupta's challenge is one of objectivity: the existence of the "shmamiked" network of concepts threatens the objectivity of facts stated using the unshmamiked network. But the challenge can be repelled given a proper understanding of objectivity itself.

Metaphysics is sensitive to the conceptual tools we choose to articulate metaphysical problems. Those tools are a lens through which we view metaphysical problems; the same problems look different when we change the lens. There has recently been a shift to "postmodal" conceptual tools: concepts of ground, essence, and fundamentality. This shift transforms the debate over structuralism in the metaphysics of science and philosophy of mathematics. Structuralist theses say that patterns are "prior" to the nodes in the patterns. In modal terms this would mean that the nodes cannot vary independently of the pattern. But its postmodal meaning is unclear. Does it mean, e.g., that a fundamental account of reality somehow speaks only of patterns? What would that mean? Three structuralist positions are examined through a postmodal lens: nomic/causal/dispositional essentialism, structuralism about individuals (e.g., structural realism, e.g., ante rem mathematical structuralism), comparativism about quantities. The question of when theories are equivalent, and how that impacts the debate over structuralism, is also discussed.