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A NOTE ON OCKHAM'S THEORY OF THE MODES OF COMMON PERSONAL SUPPOSITION The last half of this century has seen an amazingly energetic and resourceful effort to understand Ockham's supposition theory. The result is that we are much more sophisticated in our approach to the subject today than anybody could have been before. Yet, despite the fact that we now have, not only critical editions and translations of Ockham's logic texts, but also elaborately formal reconstructions of the theory of supposition itself,1 there is no clear consensus about what Ockham was up to in presenting his theory ofthe Modes of Common Personal Supposition (hereafter, following Alfred Freddoso,2 "MCPS"). Beginning with the account Philotheus Boehner offers in his Medieval Logic,3 the clearest and most intriguing suggestion has been that Ockham's theory ofMCPS is a theory ofquantification. According to that theory both the subject term and the predicate term of each ofthe standard categorical propositions, A, E, I and O, are quantified , either explicitly, as is the case with the subject term of this A proposition, (1) Every man is an animal 1 Graham Priest and Stephen Read, "The Formalization of Ockham's Theory of Supposition," Mind 86 (1977), 109-13; 'Merely Confused Supposition ," Franciscan Studies 40 (1980), 265-97. John Corcoran and John Swiniarski , "Logical Structures ofOckham's Theory of Supposition," Franciscan Studies 38 (1978), 161-83. 2 Alfred J. Freddoso and Henry Schuurman, trans., Oclcfiam's Theory of Propositions: Part U of Summa Logicae (Notre Dame: 1980), "Introduction" by Alfred J. Freddoso. 3 Manchester University Press, 1952. 82GARETH MATTHEWS or else implicitly, as with its predicate term. The predicate-term quantification would be made explicit by re-writing (1) as (2)Every man is some animal. Now Ockham's story about MCPS, on this interpretation, identifies the relevant quantifications in (l)/(2) by reference to the following two expansions: (3)This man is an animal and that man is an animal and ... (4)Every man is this animal or that animal or ... Thus when Ockham tells us that we can "descend to" (3) from (1) because the subject term in (1) has confused, distributive suppositon, he is identifying a mode of quantification by reference to a materially equivalent expansion that eliminates the quantifier, 'every.' And when he tells us we can "descend to" (4) from (1) because the predicate term has merely confused supposition, he is (according to this same interpretation ofMCPS) identifying the mode of an implicit predicate quantifier by reference to a materially equivalent expansion that brings out its force. Is this right? Is Ockham's theory ofMCPS really a theory ofquantification ? Many reasons have been offered for saying "No." Three seem especially significant. First, if Ockham's story about MCPS were meant to be a quantification theory, the conjunctive and disjunctive propositions he tells us we can descend to would have to be taken as (materially) equivalent to the original propositions from which they are derived. But Ockham never claims equivalence. And thus he does not himself offer his theory of MCPS as a quantification theory.4 Second, the descent Ockham offers from the O proposition, (5)Some man is not an animal as part of his effort to show that its predicate term, 'animal,' has confused , distributive supposition is this: 4 Gareth B. Matthews, "Suppositio and Quantification in Ockham," Nous 9 (1973), 13-24. Modes of Common Personal Supposition83 (6) Some man is not this animal and some man is not that animal and ... But (6) is obviously weaker than, and so not materially equivalent to, (5).5 Since Ockham was a good logician and no good logician would make such a mistake, Ockham is not to be taken as offering his "descents to singulars" as expansions that are materially equivalent to the originals. Hence, his theory of MCPS is not meant to be a quantification theory. Third, in Part II ofhis Summa Logicae Ockham explicitly provides truth conditions for many forms ofproposition, including those ofthe standard A, E, I and O forms. The account of truth conditions he offers does indeed make use of the idea of supposition. In giving truth conditions he says things like "the subject...
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