Natural Motion in Inanimate Bodies

The Thomist 71 (2007): 555-76 NATURAL MOTION IN INANIMATE BODIES THOMAS LARSON Saint Anselm College Manchester, New Hampshire I. INTRODUCTION: A STRONG TREND IN MODERN ARISTOTELIAN SCHOLARSHIP WHAT DOES ARISTOTLE MEAN when he says in the second book of the Physics that nature is a principle of motion belonging to a body essentially? Among modern scholars of Aristotle there exists a good deal of disagreement on this point. One trend is to understand the internal source of motion as a kind of efficient cause. Daniel Graham is one scholar who clearly articulates this position. For example, Graham claims that, according to the second book of the Physics, "[w]hile forced motions are brought about by external agents, natural motions are brought about by the agency of the thing itself."1 According to Graham, "[a]s an inherent source of change and rest, a nature is already an efficient cause."2 Graham claims that the teaching of the second book of the Physics is that nature is a principle, belonging essentially to a body, that "originates" the motion of the body,3 and he thinks that only self-motion qualifies as natural motion. T. H. Irwin also takes "origin" (his translation of "arche") of motion as an efficient cause that initiates a change. He notes, for 1 Aristotle's Physics: Book VIII, trans. with commentary by Daniel Graham (Oxford: Clarendon Press: 1999), xiii. 2 Ibid. 3 Ibid., xv. 555 556 THOMAS LARSON example, the difficulty that Aristotle (in Physics 2.1) seems to imply two things: on the one hand, he seems to imply that form and matter are efficient causes, "since they are origins of change"; on the other hand, he makes a clear distinction between formal and material causes, and this would imply that form and matter are not efficient causes.4 According to Irwin, since matter and form are principles of change, they must be taken as efficient causes of motion. According to John M. Rist, book 2 of the Physics presents nature as a principle of life and self-motion. Rist notes that in book 8 (255a5ff.), Aristotle says that though elements and inanimate bodies are natural, they are not self-movers, "[b]ut in Physics 2, the elements are included with living things without comment, as containing the principle of motion within themselves and intrinsically."5 The two passages are the source of the following issue: although in Physics 2 the study of nature deals with those subjects which contain the principle of motion and rest within themselves intrinsically, Aristotle does not identify a class of self-movers (animals and men) within 'nature' and treat them separately from plants and the four elements. Yet, according to Physics 8, these last groups, though natural and containing the principle of motion and rest within themselves, are not self-movers. Once Aristotle has made this distinction, of course, he should tell us in what other sense plants and animals "contain the principle ofmotion and rest within themselves intrinsically."6 4 T.H. Irwin, Aristotle's First Principles (Oxford: Clarendon Press, 1988), 9 (emphasis added). Irwin goes on to argue for interpreting matter, form, and final causes as abbreviated accounts of efficient causality: "The appearance of four causes instead of one seems to result from incomplete specifications of the causes and effects. If nothing more can be said for Aristotle's doctrine of four causes, then it does not describe four objectively different causes, but only four ways to describe the cause; and three of these ways are mere abbreviations of the fourth cause." According to Irwin, Aristotle cannot defend the claim that "the formal and material causes are different types of causes from the efficient cause", but "he can still reasonably argue that they are different types of efficient causes, differing from each other, though not from all types of efficient cause" (ibid., 96). 5 John M. Rist, The Mind ofAristotle: A Study in Philosophic Growth (Toronto, Buffalo, London: University of Toronto Press, 1989), 123. 6 Ibid., 124 (emphasis added). NATURAL MOTION IN INANIMATE BODIES 557 Note that in this passage Rist takes it as obvious that in book 2 of the Physics nature is an intrinsic efficient...