1 For example, Ross uses all three translations of dunamis in his translation of Book ix of the Metaphysics (Barnes (ed.) 1984). 2 Both Ross and Bonitz attempt to provide consistent interpretations of dunamis. by distinguishing two senses of the term. They differ concerning what those two senses are. Ross thinks that Aristotle distinguished between a power of a substance which is a source of change in another thing (transeunt dunamis)
and a potentiality which is the capacity that a substance has to pass into a new state of itself (immanent dunamis). However, Ross acknowledges that Aristotle's discussion in Book 17c does not consistently maintain this distinction. Concerning Aristotle's argument with the Megarians, Ross comments "It may be noted that though this discussion occurs in the section devoted to transeunt dunamis, it really refers to immanent dunamis, potentiality not power" (Ross, 1924, Vol. cxxvi-cxxvii). Bonitz holds that Aristotle distinguishes dundmis in the sense of a power to move from dunamis in the sense of possibility. (Index Aristotelicus s.v. 8vvaues) However, Bonitz also remarks that Aristotle does not maintain this distinction consistently. And, interestingly enough, he mentions just the passage we are interested in, and that Ross found problematic for his interpretation—Book 17c, chapter 3. Bonitz thinks that while Aristotle should be talking about dunamis as power in Book IX, 3, he mixes in dunamis as potentiality which for Bonitz, is possibility. Hence, Aristotle's debate with the Megarians proves problematic for both of their interpretations of dunamis. In Metaphysics v 12, Aristotle distinguishes dunamis as the capacity to change another or to be changed from the modal notions possible and impossible (1019b22-32). 4 Ide argues that the biconditional relationship between capacities and possibilities was a thesis in early Aristotle and one that he gave up in Metaphysics ix. Ide concedes that it is present in chapters 3 and 4. See Ide 1992.
5 Scholars traditionally have tried to flesh out the position of the Megarians by looking at the "Master Argument" of Diodorus Cronus, on the assumption that Diodorus Cronus was a Megarian. Sedley (1977) has argued convincingly, however, that Diodorus Cronus was not a Megarian but belonged to a rival school, and that he could only have influenced Aristotle for the last decade of Aristotle's life. We are left with conjecture. 6 This epistemic motivation for the Megarian position was suggested by Martha Nussbaum. 7 The issue between Aristotle and the Megarians concerns whether or not the capacities and powers of substances exist independently of their exercise at a given time. It is necessary to add the temporal clause "at a given time" because, on my interpretation of the priority of actuality, Aristotle's own position is that the existence of a dunamis depends upon the existence of the corresponding actuality; the capacity of sight depends upon the activity of seeing. Aristotle does not believe, however, as the Megarians apparently did, that a particular dunamis can only exist if and while it is being actualized. For the Megarians a person's capacity for sight exists only while she is actually
seeing; for Aristotle, a person's capacity for sight depends upon the existence of the kind of activity towards which it is directed, but the person need not be looking at anything.
8 See Bumyeat 1984, p. 65.
9 It is worth emphasizing that Protagoras has a perfectly consistent position available to him. Suppose that a color looks green to you and brown to me. Protagoras could hold that as long as these appearances last then the color has the capacity to look green to you and brown to me. Without further argument, Aristotle's claim that Protagoras flouts the principle of non-contradiction can also be described as Aristotle's failure to maintain relativism consistently. 10 Aristotle's next criticism concerning the Megarian account of perception follows the pattern of the Techne Argument (1047a6-10). If the ability to see is a dunamis that exists only when a person is seeing (as the Megarians would have it), then when a person is not actually seeing, she can no longer see. She would be blind, Aristotle adds, many times a day. But blindness is caused by special factors like illness, and on the Megarian account there is no explanation for the "blindness" or incapacity to see that according to them afflicts everyone everyday.
i1 Both Ide 1992, and Burnyeat 1984 translate a8uuaros as "impossible".
12 On my proposed interpretation of the Immobility Argument, the second premise states a connection between powers and possibilities, which Aristotle wants to endorse. Clearly, the Megarians could reject this premise. If they did,
then they would still have to face the first two arguments, which do not rely upon any modal implications of dunamis.
13 Ide 1992 disagrees on both points. He argues instead that Aristotle changed his mind about the relationship between capacities and possibilities, and that the refutation of the Megarians is a remnant of his earlier view.
14 Here, as in my interpretation of the Immobility Argument, Aristotle is connecting talk of capacities with modal language using words that can be translated either as capacity/possibility or incapacity/impossibility. I read the passage as providing a criterion for when a substance has a capacity, although it could be read as a test for possibility. That my reading is correct is shown by the fact that 8vvaT69 is correlated with ivtpyua, a term that Aristotle matches with capacity not possibility, and by his examples, which are classic examples of capacities.
15 In this section I discuss just one condition on potentiality. Later, in Book ix, 7 Aristotle adds further conditions on potentiality. However, those further conditions require separate treatment.