Three claims about essential properties are frequently advanced in recent discussions: (1) a property belongs essentially to a thing only if that thing would cease to exist without that property, (2) an essential property is explanatory, And (3) an essential property is such that it must belong to everything to which it belongs. I argue that the "only if" in (1) cannot be changed to "if and only if" and (1) needs to be supplemented by (2), And that (2) is (...) an indispensable feature of aristotle's view of essential properties and that it casts doubt on (3), Although (2) is usually assumed to provide a reason for (3). (shrink)

In lieu of an abstract, here is a brief excerpt of the content:Notes and Discussions ARISTOTLE'S "DE MOTU ANIMALIUM" AND THE SEPARABILITY OF THE SCIENCES In contrast to Plato's vision of a unified science of reality and with a profound effect on subsequent natural science and philosophy, Aristotle urges in the Posterior Analytics and elsewhere that scientific knowledge is to be pursued in limited, separable domains, each with its own true and necessary first principles for the explanation of a discrete (...) range of phenomena, that is, accepted observations and beliefs, from which its investigations are launched (An. Pr. 46al7ff.; An. Post. 74b25, 76a26-3 o, 84b14-18, 88a31; Cael. 3o6a6ff.; Gen. An. 748a7ff.). In an early introduction to a course of lectures on the natural sciences, Aristotle also indicates the order in which those sciences ought to be presented (Mete. 338a2o-~9, 339a5-9; cf. Cael. 268al6, Part. An. 644b~2ff.). The plan is to start with a general discussion of change and motion, then progress to studies of specific natural phenomena, ending with the many species of plants and animals. In the theory of demonstration in Posterior Analytics 1, which is concerned with the organization, justification, and teaching of a finished science, Aristotle maintains that terms cannot ordinarily cross genera; for example, geometry cannot provide demonstrations of truths of arithmetic or aesthetics. Demonstration of a theorem of some one science by means of another can be accomplished when and only when the sciences are related as "subordinate " to "superior" (75b14-17), for example, as harmonics to arithmetic or optics to geometry. A superior science may supply the "reason" for a "fact" known to obtain in the subordinate science (78b34-79a6). Evidently at least part of what he has in mind is the relation between pure and applied sciences.' Aristotle's practice as well as a number of methodological remarks ' See ThomasAquinas,In Post. An. 50.1,15.131, 50.1.25,as wellasJ. Barnes'snoteson An. Post. 78b34,in Aristotle'sPosteriorAnalytics (Oxford:OxfordUniversityPress,1975).For relevant background see Ian Mueller,"Ascendingto Problems:Astronomyand Harmonicsin Republic VII," inJohn Anton,ed., Scienceand the Sciencesin Plato (Albany:StateUniversityof NewYork Press, 1979). [65] 66 HISTORY OF PHILOSOPHY suggest also that the strictures of the Posterior Analytics are not intended to prohibit the heuristic use of material from other disciplines in research (see e.g., Top. 1.14; Part An. 639b17ff., 641a6-14, 642alo-14, 645b15-2o; Ph. 192b8-34, 199a8-21, 199a33-b5). The requirements for science laid down here are very strict, and it is sometimes maintained that Aristotle violates them himself to some degree in other works, but it is not usually believed that he ever denies the separability of the sciences in general. Martha C. Nussbaum has recently presented a lively challenge to this concensus? She argues that Aristotle's late, little known work De Motu Animalium represents a radical but "deliberate and fruitful" rejection of his earlier philosophy of science as enunciated in the Organon and not seriously questioned in other, subsequent writings. Her claim is that in his mature thought about the sciences Aristotle arrives at a significantly "less departmental and more flexible picture of scientific study" (p. 113) and comes to hold that "no inquiry is genuinely separable from a whole group of interlocking studies, and no being can be extensively studied without an account of its placement in the whole of nature" (p. 164). Nussbaum's conclusion is probably not intended to be as Platonic as it may appear at first blush, for she seems actually to be speaking only of connections between sciences of different substances. There is no suggestion that the study of beauty or health or geometry, say, is on a par with the sciences of substances. Nor does she suggest that Aristotle wavers in his conviction that there are fundamental cleavages between the practical and theoretical sciences, which will make a full-blown science of ethics-politics look very different from the demonstrative science of meteorology, for example. Nevertheless, even if limited to the natural sciences of substances, her claim remains an important and interesting one. She holds, more specifically, that Aristotle departs from his earlier position as follows: (1) He recognizes that the biological study of various modes of local motion... (shrink)