Though Arthur Prior is now best known for his founding of modern temporal logic and hybrid logic, much of his early philosophical career was devoted to history of logic and historical logic. This interest laid the foundations for both of his ground-breaking innovations in the 1950s and 1960s. Because of the important rôle played by Prior's research in ancient and medieval logic in his development of temporal and hybrid logic, any student of Prior, temporal logic, or hybrid logic should be (...) familiar with the medieval logicians and their work. In this article we give an overview of Prior's work in ancient and medieval logic. (shrink)

In his treatise on sophisms, the medieval logician and philosopher J. Buridan expounded a theory on what we have come to call semantic paradoxes. His theory has not yet been fully understood. The present paper aims at showing that Barwise's and Etchemendy's considerations on paradoxes (founded upon Aczel's non-well-founded sets) provide the framework for an improved understanding. Barwise's and Etchemendy's account is contrasted with Kripke's. Finally, a recent analysis of Buridan's position by Epstein is criticized.

The traditional model theory of first-order logic assumes that the interpretation of a formula can be given without reference to its deductive context. This paper investigates an interpretation which depends on a formula's location within a derivation. The key step is to drop the assumption that all quantified variables must have the same range and to require only that the ranges of variables in a derivation must be related in such way as to preserve the soundness of the inference rules. (...) With each (consistent) derivation there is associated a Buridan-Volpin (orBV) structure [M, {r(x)}] which is simply a Tarski structureM for the language and a map giving the ranger(x) of each variablex in the derivation. IfLK* is (approximately) the classical sequent calculusLK of Gentzen from which the structural contraction rules have been dropped, then our main result reads: If a set of first-ordered formulas has a Tarski modelM, then from any normal derivationD inLK* of can be constructed aBV modelM D=[M, {r(x)}] of where each ranger(x) is finite. (shrink)

A syntactically correct number-specification may fail to specify any number due to underspecification. For similar reasons, although each sentence in the Yablo sequence is syntactically perfect, none yields a statement with any truth-value. As is true of all members of the Liar family, the sentences in the Yablo sequence are so constructed that the specification of their truth-conditions is vacuous; the Yablo sentences fail to yield statements. The ‘revenge’ problem is easily defused. The solution to the semantical paradoxes offered here (...) revives the mediaeval cassatio approach, one that largely disappeared due to its incomprehending rejection by influential contemporary writers such as William Shyreswood and Thomas Bradwardine. The diagnosis readily extends to the set-theoretic paradoxes. (shrink)

Consideration of a paradox originally discovered by John Buridan provides a springboard for a general solution to paradoxes within the Liar family. The solution rests on a philosophical defence of truth-value-gaps and is consistent (non-dialetheist), avoids ‘revenge’ problems, imports no ad hoc assumptions, is not applicable to only a proper subset of the semantic paradoxes and implies no restriction of the expressive capacities of language.

For Jizang (549−623), a prominent philosophical exponent of Chinese Madhyamaka, all things are empty of determinate form or nature. Given anything X, no linguistic item can truly and conclusively be applied to X in the sense of positing a determinate form or nature therein. This philosophy of ontic indeterminacy is connected closely with his notion of the Way (dao), which seems to indicate a kind of ineffable principle of reality. However, Jizang also equates the Way with nonacquisition as a conscious (...) state of freedom from any attachment and definite understanding whatsoever. The issue then becomes pressing as to how we are to understand Jizang's notion of the Way. Does it indicate some metaphysical principle or reality? Is it actually a skilful expedient to lead one to the consummate state of complete spiritual freedom? How is this issue related to Jizang's conception of ontic indeterminacy? In this book chapter, I examine Jizang's key writings in an attempt to clarify his ontological position. (shrink)