The Law of Non-Contradiction and Aristotle’s Epistemological Realism

The Thomist 66 (2002): 457-71 THE LAW OF NON-CONTRADICTION AND ARISTOTLE'S EPISTEMOLOGICAL REALISM THOMAS V. UPTON Gannon University Erie, Pennsylvania IN HIS RECENT BOOK, Principles andProofs, Richard McKirahan claims the following about the law of non-contradiction: "LEM [Law of Excluded Middle] and LNC [Law of NonContradiction ] hold everywhere because all sciences (epistemai) are concerned with things-that-are, and these principles apply to all things-that-are (Meta. G, 3, 1005a22-28)."1 I believe McKirahan is correct in his claim that the law of noncontradiction applies universally to things-that-are. However, McKirahan himself does not explain how or why this is so. In this paper, I intend to offer an interpretation of how Aristotle thought the law of non-contradiction was applicable to all things-that-are in such a way as to provide a significant part of the foundation for all of the particular sciences (epistemai), which must assume the truth of this law. I will argue that the law of noncontradiction is a first principle that is both prior and most intelligible in itself and prior and most intelligible to us. I will then suggest one of the ways in which the law, as a law of being, relates to the DeAnima's account of nous and thereby governs for Aristotle the way we must think about being.2 I will conclude by 1 Richard D. McKirahan, Jr., Principles and Proofs (Princeton: Princeton University Press, 1992), 75. 2 On the law of non-contradiction as a law of thought, see Thomas V. Upton, "Psychological and Metaphysical Dimensions ofNon-Contradiction inAristotle," The Review ofMetapbysics 36 (1983): 591-606; and "Aristotle on Hypothesis and the Unhypothesized First Principle," The Review ofMetapbysics 39 (1985): 283-301. See also Jonathan Barnes, 457 458 THOMAS V. UPTON suggesting that part of the significance of the role of the law for Aristotle is that it dearly indicates that he believed in what is traditionally called metaphysical realism,3 L THE CONTEXT OF ARISTOTLE'S PRESENTATION OF THE LAW OF NON-CONTRADICTION The context of Aristotle's presentation and discussion of the law of non-contradiction in Metaphysics G is his discussion of the subject with which first philosophy (metaphysics) is concerned. He begins this discussion by maintaining that there is a science (ElWJTtjµTj) that examines being as being (To OV UOV) and the essential (1mff auTo) properties of being as being. He contrasts the science of being, which examines the whole of being as being (£m01ucnc;). The first philosopher is said by Aristotle to be higher (avwTf.ptiJ [Metaphys. G.3.1005a34]) than the physicist, for the first philosopher studies the whole (kathalou) of being and first substance (nEpi Tfjv npWTflV oucrfov [Metaphys. G.3.1005a35]). In general, the significance of the context of Aristotle's presentation of the law of non-contradiction is as follows. The context in general is the contrast between the particular sciences and the general science of being as being. Aristotle emphasizes two points in this contrast. First, the science of being as being studies the whole of being, whereas the particular sciences are restricted to the study of one, primary genos tou ontos. Second, LAW OF NON-CONTRADICTION 461 the science of being as being, which is based on the study of substance as the focal reference of being, cannot be restricted to physical, sensible substances, since the first philosopher is said to be higher than the physicist-philosopher, and his study is not restricted to phusis, as the physicist-philosopher's study is. II. FORMULATIONS OF lHE LAW OF NON-CONTRADICTION Somewhat surprisingly, in spite of the focal reference of substance, Aristotle uses somewhat different formulae for the law of non-contradiction in Metaphysics G. (1) First of all, he uses the following formula: "it is impossible for the same thing both to inhere and not to inhere in the same thing at the same time and in the same respect" (Metaphys. G.3.1005b19-20). (2) Next, he restates the first formula in a slightly different way: "[if] it is not possible for opposites to inhere in the same thing at the same time" (Metaphys. G.3.1005b26-27...