In this paper, I will describe a technique for generating a novel kind of semantics for a logic, and explore some of its consequences. It would be natural to call the semantics produced by the technique in question ‘many-valued'; but that name is, of course, already taken. I call them, instead, ‘plurivalent'. In standard logical semantics, formulas take exactly one of a bunch of semantic values. I call such semantics ‘univalent'. In a plurivalent semantics, by contrast, formulas may take one (...) or more such values. The construction I shall describe can be applied to any univalent semantics to produce a corresponding plurivalent one. In the paper I will be concerned with the application of the technique to propositional many-valued logics. Sometimes going plurivalent does not change the consequence relation; sometimes it does. I investigate the possibilities in detail with respect to small family of many-valued logics. (shrink)

Such contradictions arise “at the limits of thought” in the following sense: we have reason to set boundaries to certain conceptual processes, which, however, turn out to actually cross those boundaries. The boundaries cannot be crossed, yet they can, for they are crossed. For example, Kant regarded noumena as beyond the limit of the conceivable, yet he made judgments about them, so he did conceive of them. For another example, Russell’s theory of types cannot be expressed, yet he does express (...) it. And so on, from Aristotle’s notion of prime matter to Derrida’s différance. The boundaries that cannot be but are crossed may concern iteration, expression, cognition, or conception. In most cases, a single argument pattern is operative, according to Priest. He calls it the Inclosure Schema [=IS]. It is a contradiction-generating mechanism that works as follows: suppose we define a set Ω, on the basis of a condition φ ); suppose that Ω exists and that it has property ψ. Next, suppose we can define a function δ such that, for any subset x of Ω that has property ψ, we have both δ ∉ x and δ ∈ Ω. As Ω is a subset of itself and it has ψ by hypothesis, a contradiction follows: both δ ∈ Ω and δ ∉ Ω. The two sides of the contradiction—or perhaps the operations by which they are established—are called Closure and Transcendence. ). For example, take Burali Forti’s paradox that is greater than all members of On, and therefore not an ordinal). Here Ω = On, and δ is the function that assigns to x the least ordinal greater than all members of x is both an ordinal—δ ∈ Ω, “Closure”—and not a member of x ). The condition φ is just the property of being an ordinal. (shrink)

This is a philosophical investigation of the nature of the limits of thought. Drawing on recent developments in the field of logic, Graham Priest shows that the description of such limits leads to contradiction, and argues that these contradictions are in fact veridical. Beginning with an analysis of the way in which these limits arise in pre-Kantian philosophy, Priest goes on to illustrate how the nature of these limits was theorised by Kant and Hegel. He offers new interpretations of Berkeley's (...) master argument for idealism and Kant on the antimonies. He explores the paradoxes of self reference, and provides a unified account of the structure of such paradoxes. The book concludes by tracing the theme of the limits of thought in modern philosophy of language, including discussions of the ideas of Wittgenstein and Derrida. (shrink)

General discussion of grounding, including its formal features, relations to other notions, and applications. (Originally published 2014; revised 2021).

Graham Priest presents an original exploration of questions concerning the one and the many. He covers a wide range of issues in metaphysics--unity, identity, grounding, mereology, universals, being, intentionality and nothingness--and draws on Western and Asian philosophy as well as paraconsistent logic to offer a radically new treatment of unity.

Martin Heidegger is a towering figure in the history of continental philosophy, but his work has recently been brought into productive engagement with analytic philosophy. This paper introduces and explores two channels along which such engagement has been taking place. The first is in metaphysics, where Heideggerian thought has been interpreted either as making the metaphysical concept of being literally senseless or as mandating a revision to classical logic. The second is in philosophy of mind, and more particularly in philosophy (...) of cognitive science, where Heideggerian thought has been used to mount a challenge to representational theories of mind. (shrink)