In this paper I present a new approach to the so called ars obligatoria of the thirteenth and early fourteenth century. In standard medieval disputations an opponent attacks a thesis defended by the respondent. Some thirteenth-century authors distinguish two duties that the respondent has. First, he must grant whatever seems to be true. Second, he must grant whatever follows from what he has already granted. When the first duty is overridden by the specific duty to defend a false thesis (which (...) is the main requirement of ars obligatoria), the second duty becomes the logical duty of keeping the set of one's answers consistent. A natural result of this model is the development of a concept of possibility based on the syntactic concept of formally correct inference, and not on any semantic considerations. (shrink)

In this paper we provide an interpretation of Aristotle's rule for the universal quantifier in Topics Θ 157a34–37 and 160b1–6 in terms of Paul Lorenzen's dialogical logic. This is meant as a contribution to the rehabilitation of the role of dialectic within the Organon. After a review of earlier views of Aristotle on quantification, we argue that this rule is related to the dictum de omni in Prior Analytics A 24b28–29. This would be an indication of the dictum’s origin in (...) the context of dialectical games. One consequence of our approach is a novel explanation of the doctrine of the existential import of the quantifiers in dialectical terms. After a brief survey of Lorenzen's dialogical logic, we offer a set of rules for dialectical games based on previous work by Castelnérac and Marion, to which we add here the rule for the universal quantifier, as interpreted in terms of its counterpart in dialogical logic. We then give textual evidence of the use of that rule in Plato's dialogues, thus showing that Aris... (shrink)

The study of the medieval reception of Aristotle’s Topics has largely been oriented toward debates on dialectical argumentation. And this is surely right. Nonetheless, I wish to approach John Buridan’s commentary on the Topics from another perspective, which highlights some semantic features of the set of predicates around which the work is organized. Thus, in my paper I will first reconstruct Buridan’s account of the identification of the predicates discussed in the Topics. I will argue that, for him, they are (...) different in that they reflect one or more features of the way in which definiens and definiendum relate. By doing this, I will shed light on the role the notion of definition plays in Buridan’s commentary, so that an interpretation of it as a work on definition becomes promising. In the second part of the paper, I will offer an analysis of Buridan’s first move in his commentary toward a theory of definition. It concerns the problem of whether there is a definition of definition. In examining Buridan’s answer, I will argue for the close connection between his treatment of definitions and his theory of supposition, so that distinctions among the different modes of supposition help him to disambiguate statements in their possible meanings, and thus to clarify the difficulty related to the definability of definition. (shrink)

The modern tradition of informal logic has relied heavily on accepting, modifying, or criticizing the patterns of reasoning mentioned in Aristotle's Sophistical Refutations. However, already in 1971, Stachowiak focussed his attention on the muc h neglected Topics and enumerated in his work, Rationalismus im Ursprung some of the Aristotelian rules governing the formation of definitions and principles for correct reasoning. The paper will try to examine how these principles might ap ply to informal arguments today.