This is an open access title available under the terms of a CC BY-NC-ND 4.0 International licence. It is free to read at Oxford Scholarship Online and offered as a free PDF download from OUP and selected open access locations. We need to understand the impossible. Francesco Berto and Mark Jago start by considering what the concepts of meaning, information, knowledge, belief, fiction, conditionality, and counterfactual supposition have in common. They are all concepts which divide the world up more finely than logic does. Logically equivalent sentences may carry different meanings and information and may differ in how they're believed. Fictions can be inconsistent yet meaningful. We can suppose impossible things without collapsing into total incoherence. Yet for the leading philosophical theories of meaning, these phenomena are an unfathomable mystery. To understand these concepts, we need a metaphysical, logical, and conceptual grasp of situations that could not possibly exist: Impossible Worlds. This book discusses the metaphysics of impossible worlds and applies the concept to a range of central topics and open issues in logic, semantics, and philosophy. It considers problems in the logic of knowledge, the meaning of alternative logics, models of imagination and mental simulation, the theory of information, truth in fiction, the meaning of conditional statements, and reasoning about the impossible. In all these cases, impossible worlds have an essential role to play.

Mark Jago presents an original philosophical account of meaningful thought: in particular, how it is meaningful to think about things that are impossible. We think about impossible things all the time. We can think about alchemists trying to turn base metal to gold, and about unfortunate mathematicians trying to square the circle. We may ponder whether god exists; and philosophers frequently debate whether properties, numbers, sets, moral and aesthetic qualities, and qualia exist. In many philosophical or mathematical debates, when one side of the argument gets things wrong, it necessarily gets them wrong. As we consider both sides of one of these philosophical arguments, we will at some point think about something that's impossible. Yet most philosophical accounts of meaning and content hold that we can't meaningfully think or reason about the impossible. In The Impossible, Jago argues that we often gain new information, new beliefs and, sometimes, fresh knowledge through logic, mathematics and philosophy. That is why logic, mathematics, and philosophy are useful. We therefore require accounts of knowledge and belief, of information and content, and of meaning which allow space for the impossible. Jago's aim in this book is to provide such accounts. He gives a detailed analysis of the concept of hyperintensionality, whereby logically equivalent contents may be distinct, and develops a theory in terms of possible and impossible worlds. Along the way, he provides a theory of what those worlds are and how they feature in our analysis of normative epistemic concepts: knowledge, belief, information, and content.

What makes up reality, and how? What kinds of entity are fundamental to reality, and how do dependent entities depend on the fundamental ones? How does one entity metaphysically ground another? These questions are central to contemporary metaphysics. The papers in this collection, written by a new generation of metaphysicians, address these and related questions. They investigate the metaphysical concepts of grounding and fundamentality, and the relationship between the fundamental and all the other parts of reality. Together, these papers represent the cutting-edge of a central topic in contemporary metaphysics.

Mark Jago presents and defends a novel theory of what truth is, in terms of the metaphysical notion of truthmaking. This is the relation which holds between a truth and some entity in the world, in virtue of which that truth is true. By coming to an understanding of this relation, he argues, we gain better insight into the metaphysics of truth. The first part of the book discusses the property being true, and how we should understand it in terms of truthmaking. The second part focuses on truthmakers, the worldly entities which make various kinds of truths true, and how they do so. Jago argues for a metaphysics of states of affairs, which account for things having properties and standing in relations. The third part analyses the logic and metaphysics of the truthmaking relation itself, and links it to the metaphysical concept of grounding. The final part discusses consequences of the theory for language and logic. Jago shows how the theory delivers a novel and useful theory of propositions, the entities which are true or false, depending on how things are. A notable feature of this approach is that it avoids the Liar paradox and other puzzling paradoxes of truth.