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The Principle of Sufficient Reason (PSR) says that all contingent facts must have explanation. In this 2006 volume, which was the first on the topic in the English language in nearly half a century, Alexander Pruss examines the substantive philosophical issues raised by the Principle Reason. Discussing various forms of the PSR and selected historical episodes, from Parmenides, Leibnez, and Hume, Pruss defends the claim that every true contingent proposition must have an explanation against major objections, including Hume's imaginability argument and Peter van Inwagen's argument that the PSR entails modal fatalism. Pruss also provides a number of positive arguments for the PSR, based on considerations as different as the metaphysics of existence, counterfactuals and modality, negative explanations, and the everyday applicability of the PSR. Moreover, Pruss shows how the PSR would advance the discussion in a number of disparate fields, including meta-ethics and the philosophy of mathematics.

Leibniz often refers to the Principle of Sufficient Reason as something like a first principle. In some texts, however, he attempts to give positive arguments in its favor. I examine two such arguments and find them wanting. The first argument has two defects. First, it is question-begging; and, second, when the question-begging step is excised, the principle that one can derive is highly counterintuitive. The second argument is valid, but it has the defect of reaching only a nearly trivial conclusion.

This paper explores the prospects of combining two views. The first view is metaphysical rationalism (the principle of sufficient reason): all things have an explanation. The second view is metaphysical essentialism: there are real essences. The exploration is motivated by a conflict between the views. Metaphysical essentialism posits facts about essences. Metaphysical rationalism demands explanations for all facts. But facts about essences appear to resist explanation. I consider two solutions to the conflict. Exemption solutions attempt to exempt facts about essences from the demand for explanation. Explanation solutions attempt to explain facts about essences. I argue that exemption solutions are less promising than explanation solutions. I then consider how explanation solutions might be developed. I suggest that a \"generative\" approach is most promising. I tentatively conclude that the prospects for combining metaphysical rationalism and metaphysical essentialism turn on the viability of a generative approach. This sets the agenda for defending the combination as well as the more general project of explaining essences.

I argue against a principle that is widely taken to govern metaphysical explanation. This is the principle that no necessary facts can, on their own, explain a contingent fact. I then show how this result makes available a response to a longstanding objection to the Principle of Sufficient Reason—the objection that the Principle of Sufficient Reason entails that the world could not have been otherwise (i.e. that all facts are necessary).

Normativity involves two kinds of relation. On the one hand, there is the relation of being a reason for. This is a relation between a fact and an attitude. On the other hand, there are relations specified by requirements of rationality. These are relations among a person's attitudes, viewed in abstraction from the reasons for them. I ask how the normativity of rationality—the sense in which we ‘ought’ to comply with requirements of rationality—is related to the normativity of reasons—the sense in which we ‘ought’ to have the attitudes what we have conclusive reason to have. The normativity of rationality is not straightforwardly that of reasons, I argue; there are no reasons to comply with rational requirements in general. First, this would lead to ‘bootstrapping’, because, contrary to the claims of John Broome, not all rational requirements have ‘wide scope’. Second, it is unclear what such reasons to be rational might be. Finally, we typically do not, and in many cases could not, treat rational requirements as reasons. Instead, I suggest, rationality is only apparently normative, and the normativity that it appears to have is that of reasons. According to this ‘Transparency Account’, rational requirements govern our responses to our beliefs about reasons. The normative ‘pressure’ that we feel, when rational requirements apply to us, derives from these beliefs: from the reasons that, as it seems to us, we have.

This essay is about love and its place in ethics. It argues that there is no one it is irrational to love, that it is rational to act with partiality to those we love, and that the rationality of doing so is not conditional on love. It follows that Anscombe and Taurek are right: you are not required to save three instead of one, even when those you could save are perfect strangers.

I argue for a novel interpretation of Leibniz’s conception of the kind of contingency that matters for freedom, which I label ‘agential contingency.’ In brief, an agent is free to the extent that she determines herself to do what she judges to be the best of several considered options that she could have brought about had she concluded that these options were best. I use this novel interpretation to make sense of Leibniz’s doctrine that the reasons that explain free actions are merely inclining and not necessitating.

The variably strict analysis of conditionals does not only largely dominate the philosophical literature, since its invention by Stalnaker and Lewis, it also found its way into linguistics and psychology. Yet, the shortcomings of Lewis–Stalnaker’s account initiated a plethora of modifications, such as non-vacuist conditionals, presuppositional indicatives, perfect conditionals, or other conditional constructions, for example: reason relations, difference-making conditionals, counterfactual dependency, or probabilistic relevance. Many of these new connectives can be treated as strengthened or weakened conditionals. They are definable conditionals. This article develops a technique to infer the logic for such definable conditionals from the known logic of the underlying defining conditional. The technique is applied to central examples. The results show that a large part of the zoo of conditionals arises from a basic conditional—a constant nucleus of the different contextual and conceptual variations of variably strict conditionals.

Leibniz holds that there are no two perfectly similar things, a doctrine he calls the Principle of the Identity of Indiscernibles (the PII). What is his attitude toward its modal status? Most commentators hold that the principle is best understood as a necessary truth because it is allegedly entailed by doctrines such as the conceptual containment theory of truth, the Principle of Sufficient Reason (the PSR), and the denial of purely extrinsic denominations, which are arguably regarded by Leibniz as necessary truths. In this paper, I argue against this consensus and show that (1) neither the conceptual containment theory of truth, nor the PSR, nor the denial of purely extrinsic denominations give Leibniz a good reason to hold that the PII is necessary; (2) Leibniz says that the PII is contingent in the correspondence with Clarke and not for dialectical reasons; and (3) the argument that Leibniz gives for the PII in §21 of his Fifth Letter to Clarke has been misunderstood; properly interpreted, it gives Leibniz a cogent argument rooted in some of his most important doctrines for the conclusion that the PII is a contingent truth.

The Principle of Sufficient Reason must be justified dialectically: by showing the disastrous consequences of denying it. We formulate a version of the Principle that is restricted to basic natural facts, which entails the obtaining of at least one supernatural fact. Denying this principle results in extreme empirical skepticism. We consider six current theories of empirical knowledge, showing that on each account we cannot know that we have empirical knowledge unless we all have a knowledge of the PSR. We consider objections based on NeoHumeanism and the essentiality of origins, and we consider the possibility that we have empirical knowledge without knowing it.