Online research in philosophy

In Contradiction advocates and defends the view that there are true contradictions (dialetheism), a view that flies in the face of orthodoxy in Western philosophy since Aristotle. The book has been at the center of the controversies surrounding dialetheism ever since its first publication in 1987. This second edition of the book substantially expands upon the original in various ways, and also contains the author's reflections on developments over the last two decades. Further aspects of dialetheism are discussed in the companion volume, Doubt Truth to be a Liar, also published by Oxford University Press in 2006.

In the first part the paper rehearses the main arguments why to be a dialetheist (i.e. why to assume that some contradictions are true). Dialetheism, however, has been criticised as irrational or self-refutating. Therefore the second part of the paper outlines one way to make dialetheism rational assertable. True contradictions turn out to be both believable and assertable. The argument proceeds by setting out basic principles of assertion and denial, and employing bivalent truth value operators.

We address an issue recently discussed by Graham Priest: whether the very nature of truth (understood as in correspondence theories) rules out true contradictions, and hence whether a correspondence-theoretic notion of truth rules against dialetheism. We argue that, notwithstanding appearances to the contrary, objections from within the correspondence theory do not stand in the way of dialetheism. We close by highlighting, but not attempting to resolve, two further challenges for dialetheism which arise out of familiar philosophical theorizing about truth.

Dialetheism is the view that there are true contradictions. Classical dialetheism holds further the view that the law of excluded middle is indeed a logical law. Most famous dialetheists, such as G. Priest and J. Beall, are classical dialetheists; they take classical dialetheism to be the only plausible solution to the semantic paradoxes. The main contention of the paper is, however, that their views should be rejected. Based on inspecting Priest’s and Beall’s dialetheist theories from a special perspective, this paper contends that classical dialetheism has no natural and plausible way to assign truth values to various truth-ineliminable sentences, i.e., sentences whose truth-conditions essentially involve the property of being true . Several examples of such truth-ineliminable sentences are given in the paper, and two classical dialetheist strategies for assigning them truth values are inspected. This paper argues that none of these strategies is successful.

The aim of this paper is to show that Graham Priest's dialetheic account of semantic paradoxes and the paraconsistent logics employed cannot achieve semantic universality. Dialetheism therefore fails as a solution to semantic paradoxes for the same reason that consistent approaches did. It will be demonstrated that if dialetheism can express its own semantic principles, a strengthened liar paradox will result, which renders dialetheism trivial. In particular, the argument is not invalidated by relational valuations, which were brought into paraconsistent logic in order to avoid strengthened liar paradoxes.

Stephen Read has presented an argument for the inconsistency of the concept of validity. We extend Read’s results and show that this inconsistency is but one half of a larger problem. Like the concept of truth, validity is infected with what we call semantic pathology, a condition that actually gives rise to two symptoms: inconsistency and indeterminacy. After sketching the basic ideas behind semantic pathology and explaining how it manifests both symptoms in the concept of truth, we present cases that establish the indeterminacy of validity and that link this indeterminacy with the concept’s inconsistency. Our conclusion is that an adequate treatment of the semantic pathology thus revealed must deal with both of its symptoms. Further, it must extend to the occurrences of this condition elsewhere: in the concept of truth, in the other central semantic notions, and even in certain philosophical concepts outside semantics.

A dialetheia is a sentence, A, such that both it and its negation, ¬A, are true (we shall talk of sentences throughout this entry; but one could run the definition in terms of propositions, statements, or whatever one takes as her favourite truth-bearer: this would make little difference in the context). Assuming the fairly uncontroversial view that falsity just is the truth of negation, it can equally be claimed that a dialetheia is a sentence which is both true and false.