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A11. Rational dispositions

A very special variety of dispositions are the so-called rational dispositions (dynameis meta logou, cf. Met. IX 2, 1046b 2). There are several reasons for calling them rational dispositions. First, Aristotle describes these dispositions by saying that they are present in the rational part of the soul. This means that they cannot be had by non-living things, plants or mere beasts. Second, these dispositions are accompanied by a logos, a rational formula like a definition of the realisation. Third, the acts that are realisation of these dispositions come about by means of ratiocination, i.e. by means of practical syllogisms. What this means can be illustrated with the help of the art of medicine, which is Aristotle's stock example for this kind of dispositions. The “rational formula” that accompanies the art of medicine is the logos or definition of health. Starting from such a definition of the form “Health is XYZ”, the medical practitioner can deliberate which means he has to choose to heal his patients:

Health is XYZ.

XYZ will come about if I do F. I can do F.

Thus I will do F.

A special feature of rational dispositions is that they can have contrary realisations. Medical knowledge is normally used to heal patients, but an evil doctor can use that very same knowledge to kill people. Thus, the art of medicine can have effects as distinct as health and death. Therefore, the realisation of rational dispositions cannot be triggered as simply as the non-rational dispositions discussed in the preceding section. It is clear that spatial vicinity between a medical practitioner and an ill patient does not automatically lead to a realisation of the practitioner's healing disposition. First, the practitioner has to decide to activate his medical knowledge, but this is not enough. The practitioner has also to decide on his goal: Does he want his patient healthy or dead? Only then is he able to ratiocinate on possible means to the end chosen by him, which will eventually lead to appropriate actions that may bring about the patient's health or the patient's death.[1]

A12. Natures and habits

The different kinds of dynameis that I discussed up to now are not the only causal properties that Aristotle knows of. Other causal properties are natures and habits, physeis and hexeis. But what are natures for Aristotle? Aristotle often remarks that a nature, a physis, is a principle of movement.[2] Physis, thus, has the same genus as dynamis. But what is its specific difference? Aristotle spells this out in the following passage:

And I mean by dynamis not only that definite kind which is said to be a principle of change in another thing or in the thing itself regarded as other, but in general every principle of movement or of rest. For nature (physis) also is in the same genus as dynamis; for it is a principle of movement – not, however, in something else but in the thing itself qua itself. (Met. IX 8, 1049b 5-10, tr. Ross, italics mine; cf. Cael. III 2, 301b 17-19)

Thus, whereas an active power is a principle of change “in another or as another”, a physis is a principle of change in a thing “in itself qua itself ” and whereas an active power needs a complementary passive disposition in order to be realised, there is no such need for a physis. If something has a physis to do or to be F, the realisation is only dependent on the appropriate marginal conditions, but not on the spatial vicinity of the bearers of other causal properties.

Another kind of causal properties goes under the name of hexis. Like dynamis, hexis is a word with many different meanings, to which Aristotle dedicates a chapter in his dictionary of ambiguous philosophical terms (Met V 20). The noun hexis derives from the verb echein, “to have”. As this etymology indicates, a hexis is in general either the having of something or that which is had by something. As a further possible meaning, Aristotle proposes the following definition:

Hexis means a disposition (diathesis) according to which that which is disposed is either well or ill disposed, and this either in itself (kath'hauto) or with reference to something else (pros allo). (Met. V 20, 1022b 10-12)

What is of particular interest for us are the hexeis of the non-rational faculties of the soul, which determine both our emotional reactions and many of our actions. Traditionally, these hexeis are called virtues and vices: Virtues if they dispose for good acting, vices if they dispose for bad acting.

At first sight, a virtue like justice has a structure similar to a dynamis. At a given time, someone can have the virtue without acting justly, e.g., when sleeping, and when the just person is acting justly, the virtue of justice is thought to have a causal influence. Thus, virtues (and vices) are also realisable and causal properties, but Aristotle takes great pain in distinguishing nonrational virtues from rational dynameis, for we have seen that in the case of a rational dynamis, like the art of medicine, one and the same dynamis can be the cause of contrary realisations, i.e. of health and death. The art of calculating just prices is such a rational dynamis – but like medicine, this art can be used to calculate and to charge just as well as unjust prices (cf. NE V 1; Plato, Hip. min.). He who has the virtue of justice does not only know what is just, he is also inclined to do so. Thus, while a rational dynamis allows for contrary realisations, a virtue is directed to one realisation only, and while a rational dynamis needs an appropriate will and goal in order to be realised, a virtue informs the will by itself and does not need the addition of a goal of action from the outside.

  • [1] For a more detailed account cf. section 2.4
  • [2] Cf. Phys. II 1, 193a 28ff; III 1, 200b 12f; An. II 1, 412b 17; Met. V 4, 1015a 15-19; XI 1, 1059b 17f
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