This paper consists of two parts. The first criticizes the usual interpretation of the so-called existential quantifier as denoting existence. It is argued that it symbolizes “someness,” as is obvious from its definition as not-all-not, as in “Some citizens will vote,” which is analyzable as “Not all citizens will abstain from voting.” The second part of the paper argues that “existence” is fivefold: real, phenomenal, conceptual, semiotic, and fantastic. A definition and a criterion are proposed for every one of them. Real existence is identified with mutability; phenomenal existence, with occurrence in someone’s sensory experience; conceptual existence, as occurrence in a conceptual system; semiotic existence, as the ability of a sign to excite a reaction in an animal perceiving it; and fantastic existence, as occurrence in a work of fiction that contains or suggests it. Finally, a general concept of existence in a given context is defined with the help of the characteristic function of the said context. In other words, an existence predicate is defined, and so Anselm’s famous proof of the existence of God is shown to be formally correct.

Evaluating the probative merit of philosophical claims calls for assessing both their inherent plausibility and also their external harmonization with what is accepted elsewhere. However, cogent assessment of plausibility and harmonization calls for judgments of comparative weight and significance that one can make only on the basis of experience. The relevant body of experiences that is operative here is bound to differ among different individuals, who themselves are bound to occupy different points of view. This leads to a variation in philosophical judgment that is not a relativism of rationally indifferent matters of mere taste but rather a rationally cogent contextualism that requires different conclusions to be drawn from different premises.

The master argument posits a metaphysical thesis: Diodorus does away with Aristotle’s dunamis understood as a power simultaneously oriented toward being and nonbeing, and proclaims that possibilities that fail to actualize are simply nothing. The author’s contention is that this claim is not a mere application of Diodorus’ contribution to modal logic. Rather, Diodorus creates an ontologico-temporal concept of possibility and impossibility. Diodorus envisions the future as the past that the future will become. Since what will have been can never be the accomplishment of a possibility that did not obtain, and since the future is destined to become past, any futural possibility that doesn’t actualize is neither futural nor even possible.

Since Voltaire’s caricature of him in Candide, Leibniz has had the unenviable reputation of representing the worst excesses of metaphysical rationalism. Bernard Williams once characterized Leibniz’s view that ours is the best of all possible worlds—defining “best” as maximum variety by the simplest laws—as “crass” and “untruthful.” Drawing on the character of Ivan in The Brothers Karamasov, A. W. Moore recently developed Williams’s view, claiming that Leibniz’s system lacks the resources to support a connection between what for Leibniz “matters in the end, and what matters now, to us.” The author attempts to disarm Moore’s objection using Leibniz’s theory of truth and his principle of sufficient reason. More generally he argues that for Leibniz, when it comes to reconciling individual circumstance with the cosmic order of things, theodicy cannot provide any principled substitute for individual effort of will. This tempers the optimism typically associated with Leibniz’s philosophy.