Validity Conditions and Analysed Propositions

Alexander Broadie

in Introduction to Medieval Logic

Second edition

Published in print April 1993 | ISBN: 9780198240266
Published online October 2011 | e-ISBN: 9780191680137 | DOI:
Validity Conditions and Analysed Propositions

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This chapter considers the inferential power of categorical propositions where the structure of those propositions is taken into account. At the heart of the medieval theory of valid inference for analysed propositions lies an account of three ways in which two categorical propositions with the same categorematic terms may be related to each other. They may be related by opposition, equipollence, or conversion. Propositions related by opposition or equipollence have the same categorematic terms in the same order; where the relation is that of conversion the order is not the same. Equipollence is a relation of equivalence between two propositions structurally related to each other in a certain quite specific way. Opposition is not a relation of equivalence. Perhaps the best-known notion of medieval logic is that of the square of opposition, a square that medieval logicians liked and of which they drew a considerable variety.

Keywords: categorical propositions; valid inference; analysed propositions; medieval logic; opposition; equipollence; conversion; categorematic terms; square of opposition

Chapter.  12434 words. 

Subjects: Philosophy of Mathematics and Logic

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