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This chapter is a summary, emphasizing the principal themes of the book and their connections under the headings The Demarcation Problem, Milesian Science, Science and Philosophy, The Impact of Christianity, 'Logical Impossibility', Institutions, Morals and Ethics. Pervading notions are the high/low distinction, the Milesian requirements for science, and the alleged contingency of the world.

Cartesian skepticism, unlike Pyrrhonism, was total, calling into question low beliefs as well as high. Descartes himself was not a skeptic but set out the argument in its favor for the purpose of refuting it and thereby strengthening theology. His argument was only possible against a specifically medieval background, his Evil Demon being the Omnipotent Creator-Legislator (OCL) in disguise. But as the skepticism was more convincing than the refutation, this concept is still around in our day, responsible for ‘modern’ philosophy's obsession with finding ‘foundations’ for knowledge. The pattern of the Ontological Argument for the existence of God, which moves from subjective conceivability to objective existence, can still be discerned in David Chalmers's advocacy of mind-body dualism: the subjective ‘logical possibility’ of zombies purporting to show the objective reality of the schism.

This paper explores the philosophical transitions in the relations between existence and possibility in Leibniz and Kant. It begins with Leibniz’s formulation of a strictly logical notion of possibility; proceeds with Kant’s pre-critical statement in 1763 that existence is not a predicate; and ends with the Critique of Pure Reason in which the theory of possibility is constrained by the subjective conditions of experience (to supply the material for thinking possibilities) and is thus relativized to the human mind. I present Leibniz’s view of possibility against the traditional view of temporal modalities; and, in this light, his dual notion of existence. I then argue that, in Kant’s pre-critical essay of 1763, the view that existence is not a predicate is strongly related to the logical view of possibility advanced by Leibniz. I conclude with Kant’s transition to the critical period and its implications on the analysis of modality.

Judaism held that there was truly only one God, creator, warlord, and legislator, Who accomplished everything simply by willing it. Christianity retained its beliefs about God and imposed this model on the intellectual world. God's omnipotence made everything about nature contingent. Everything imaginable became ‘logically possible,’ hence could be the case should God will it. God imposed the Laws of Nature and could suspend them–miracles. Together these notions added up to the conception of “possible worlds." When gradually Greek learning revived to the point of being a rival to Christian orthodoxy, St. Thomas Aquinas worked out a compromise: Aristotle was held authoritative as to the usual behavior of Nature, including the human body; but the human soul, and truths knowable only by revelation, were the province of the Church. Thus a new membrane was hung up between high and low beliefs, this time a visible one. But it was fairly soon ruptured, notably in the Galileo case.

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.

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 explores another key element in the pre-Critical Kant’s development of an anti-logicist modal metaphysics: his doctrine that there are logically compatible predicates that are not possibly co-instantiated. First, it examines the notion of ‘ground’ in eighteenth-century German metaphysics and then it explains Kant’s rejection of the logicist theory of causal grounding: the relation of a cause to its effect is not a logical relation of conceptual containment or propositional entailment. It goes on to reconstruct Kant’s argument that, if there is what he calls ‘real conflict’ (two causes mutually cancel one another’s effects), then there are logically compatible predicates that are not possibly co-instantiated. This is another key counter-example to the logicist identification of possibility with logical consistency. ‘Real possibility’ refers to what is possible, not merely what is logically consistent.

This chapter opens with an exploration of the core theory of modality shared by three of Kant’s most important rationalist predecessors (Leibniz, Wolff, and Baumgarten), which is henceforth referred to as ‘logicism’: everything logically consistent is possible. It then focuses on their shared view that God necessarily exists because existence is contained in his essence. It examines Kant’s famous objection to the ontological argument (that existence is not a “real predicate”) in light of his rejection of this model of divine necessary existence. It argues that, correctly interpreted, the Kantian doctrine that existence is not a real predicate entails that there cannot be a being whose existence is contained in its essence. Kant’s target is not merely a certain argument for God’s existence, but a background metaphysical view of why he exists necessarily.

This chapter provides an account of how Kant understands divine freedom in relation to the creation of the world. The divine will as ‘holy’ is shaped by perfect goodness, and is unable in many significant ways to do other than it does. God’s ‘inability to do otherwise’ is not construed by Kant as a lack or impotence on the part of God. Rather, this ‘inability’ is an expression of God’s perfection. While Kant’s conception of human freedom shifts considerably, his conception of divine freedom remains largely stable across the development of his thought. Kant has a positive conception of freedom, expressed paradigmatically in divine freedom, where what matters for freedom is that the will is oriented to the good. The chapter engages in particular with Chignell and Kain, and with Kant’s distinction between real and logical possibility.

This chapter contradicts the anti-predictionism theory, which states that as long as an action is determined, it can be predicted, and vice versa. It begins by distinguishing between determinism and predictability, and juxtaposing human behavior with physical events. It then describes four types of “possibility of prediction” namely, logical possibility, logical compossibility, physical possibility, and causal composibility in light of explaining how voluntary actions can be scientifically predicted. Finally, it discusses that the causal necessity of an action is what makes it susceptible to scientific prediction, granted that the action is determined.

We learn the meaning or a word or sentence by learning some of the syntactic and semantic rules for its use. A declarative sentence expresses a proposition. A proposition is logically impossible iff it entails a contradiction; it is logically necessary iff its negation entails a contradiction; it is logically possible if it is entailed by an obviously logically possible proposition. We may discover the logical modal status of a proposition, when this is not obvious, by the methods of deducing such contradictions or by the method of reflective equilibrium. Or we may infer that a proposition is logically possible by showing that, if it were logically possible, it would probably be true. Neither ‘concept empiricism’ (that is, Hume’s claim that ‘all [conceivable] ideas are derived from impressions’), nor the verification principle, can settle issues of logical status.