Abstract

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.