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Mind-Body Interaction and Metaphysical Consistency: A Defense of Descartes EILEEN O'NEILL SIMON FOUCHER, in his Critique de la Recherche de la v~rit~ of* l'on examine en mOme-tems une partie des Principes de M. Descartes (Paris, x675 ), was one of the first to formulate an argument for the inconceivability of mind-body interaction within the system of Cartesian metaphysics.' The problem was the impossibility of making the following three claims consistent: i wish to thank Margaret Wilson, Calvin Normore, Daniel Garber, John Etchymendy, and Fred Freddoso for their helpful comments on earlier drafts of this material. I also am grateful to the students and faculty of The Graduate Center, CUNY for the opportunity to present to them a slightly different version of this paper. The final stages of my research were funded by a grant from The City University of New York PSC-CUNY Research Award Program. The editions referred to and their abbreviations are as follows: AT = Oeuvres de Descartes, ed. C. Adam and F. Tannery (Paris: L. Cerf, 1897-191o). HR = The Philosophical Works of Descartes, ed. and tr. E. S. Haldane and G. R. T. Ross (Cambridge: Cambridge Univ. Press, 1972). A = Oeuvres philosophiques de Descartes, ed. F. Alqui6 (Paris: Classiques Garnier, 1963-73). K = Descartes:PhilosophicalLetters, ed. and tr. A. Kenny (Oxford: Claredon Press, 197o). = Descartes:Discourse on Method, Optics, Geometry and Meteorology, tr. P. J. Olscamp (Indianapolis : Bobbs-Merrill, 1965). C = Descartes' Conversation with Burman, tr. J. Cottingham (Oxford: Claredon Press, 1976). T = Treatise of Man, tr. T. S. Hall (Cambridge: Harvard Univ. Press, 1972). AG = Descartes:Philosophical Writings, ed. and tr. E. Anscombe and P. Geach (London: Thomas Nelson and Sons, x954). DM = Suarez: Disputationes Metafisicas, ed. y tr. de Romeo, S~nchez y Zan6n (Madrid: Biblioteca Hispanica De Filosofia, 1962). The translations from the Latin originals are mine except where indicated. References include, wherever possible, the original version from AT, as well as an English language translation. All translations used in this paper are from HR, K, O, C, T, and AG, unless otherwise indicated. [227] 228 JOURNAL OF THE HISTORY OF PHILOSOPHY 25:2 APRIL 1987 1. Mind and body causally interact. 2. Mind and body are essentially different substances. 3. There must be essential likeness between a cause and its effect. Foucher's argument seems to have had a lasting philosophical impact. A standard approach in the history of Early Modern philosophy is to view the Rationalist and Empiricist traditions in the Seventeenth and Eighteenth Centuries as, at least in part, dialectically responding to the problematic which Foucher presented. The various views which rejected one or more of the three claims came to be known as (Spinoza's) parallelism, (Leibniz') Pre-established Harmony, (Berkeley's) Idealism, and (Malebranche's) Occasionalism . In addition, Foucher's formulation one of the main objections which is put ism today. C. D. Broad, for example, Mind and Its Place in Nature? of the Cartesian problematic is still forward against dualistic interactionexamined this argument in his The More importantly for my purposes here, the Foucher mind-body problem continues to be a charge which many contemporary commentators level against Descartes' account of psycho-physical change. Anthony Kenny, for instance, has criticized Descartes in this way, and Daisie Radner has written: "That the mind should cause a modification in the body, or the body in the mind, conflicts with what the Cartesian natural light reveals about the nature of the causal situation .... For, as Descartes himself sees the causal situation, one substance cannot produce a modification in another substance which is of an entirely different nature. ''~ Interestingly enough, Richard Watson, in his book, The Downfall of Cartesianism , has argued that most of the philosophers who faithfully carried out Descartes' program, "the Orthodox Cartesians," as Watson calls them, were never faced with the Foucher inconsistency.4 They simply did not accept claim (3): There must be essential likeness between a cause and its effect. This rejection of (3) was true at least of Robert Desgabets, in his Critique de la Critique de la Recherche de la vkrit~ (1675); Louis de la Forge, in Trait~ de l'Sme humaine (1666); Jacques Rohault, in Trait~ de physique...