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Aristotle on Genus and Differentia HERBERT GRANGER IN ARISTOTLE'S WRITINGS there are at least three accounts of the nature of genus and differentia. These accounts may be briefly described in these terms: (I) genus and differentia are radically distinct in character, and the genus is the more important element in the definition; (II) genus and differentia are very similar in character and importance; (III) genus and differentia are similar in character, but the differentia is the more important element in the definition. These accounts represent, I believe, three stages in the development of Aristotle's thought. In this paper I shall examine each account and explain, at least in part, why Aristotle adopts them. Preliminary Remarks: The Topics, especially books IV, VI, and VII, offers the most detailed discussion of genus and differentia, and it also provides evidence for all three stages. The Categories also contains evidence for each stage. The plainest evidence for the first two stages is in the Topics and Categories; and since the bulk of these works is very early,' the first two stages probably belong to early periods in Aristotle's thought. The third stage seems to be last, since it appears most clearly in the Metaphysics, a relatively late work. 2 And if it is the last stage, then the order of the other two seems reasonable. For the third stage would seem more likely to develop from a view in which genus and differentia are roughly the same in character than from one in which they ' The generally accepted view is that the Topicsis very early. See Pamela M. Huby, "The Date of Aristotle's Topics and its Treatment of the Theory of Ideas," Classical Quarterly 12 0962): 72; in n. a on p. 72 Huby notes many of the scholars who believe the Topicsto be very early. For the view that the Topicsand Categorieswere written about the same time, see: Isaac Husik, "On the Categoriesof Aristotle," PhilosophicalReview 13 (19o4): 514-28; L. M. De Rijk, "The Authenticity of Aristotle's Categories,"Mnemosyne4 (1951): 129-57. 2 For a relatively late date for the bulk of the Metaphysics,see: W. D. Ross, Aristotle's "Metaphysics ', 2 vols. (Oxford: Clarendon Press, 1924), I: xiv-xv (hereafter cited as "Met.'). [,] 2 JOURNAL OF THE HISTORY OF PHILOSOPHY 22:1 JAN 198 4, are quite distinct and in which the genus plays a more important role in the definition than the differentia. Other works, such as the Analytics and Parts of Animals, also contain important discussions of genus and differentia. On the whole, however, they do not provide any significant information, at least beyond what the Topics, Categories and Metaphysics provide, toward an account of the three stages I analyze. Other stages, besides the three I distinguish, might very well be found concerning genus and differentia, stages that might represent transitional ones between those I consider. 1 simply maintain that the three I investigate are readily discernible, when one undertakes an examination of Aristotle's comments on genus and differentia. The evidence for these three incompatible accounts can be found in the same work, even, as it turns out, in the same chapter in some cases) Why then do I prefer to represent them as three stages in Aristotle's thought, instead of incompatible views he holds simultaneously? Since the accounts do conflict, and if they can truly be attributed to Aristotle, it seems only reasonable and charitable, even if some of the evidence for them arises in the same work, to argue that they represent different stages in his thought, at least initially and until additional contrary evidence is available, rather than to accuse him of holding simultaneously incompatible views. Moreover, it is certainly possible that many of Aristotle's works contain material from various periods in his career. For it is a plausible and generally accepted view that his extant works are lecture notes or provided, the memoranda for bis actual lectures and that he would have used them over long periods, during which he would probably revise them periodically and introduce new material into them.4 In addition, it is not at all surprising that the Topicscontains evidence for many different periods...