LECTURE 13 (198 b 34-199 a 33)

IT IS DEMONSTRATED THAT NATURE ACTS FOR AN END

             255. Having stated the opinion and argument of those who say that nature does not act for an end, he here disproves this position.

             He does this first through appropriate arguments, and secondly, where he says, 'Now mistakes come to pass . . .' (199 a 33), through arguments taken from those things from which the opponents tried to prove the contrary position.

             256. Concerning the first point he sets forth five arguments. The first is as follows. Everything which happens naturally either happens in every instance or in most instances. But nothing which happens by fortune or by that which is per se vain, i.e., by chance, happens in every instance or in most instances. For we do not say that in the winter it rains frequently by fortune or by chance. But if it rains frequently during the dog days, we would say that this happens by chance. And in like manner, we do not say that it happens by chance that there is heat during the dog days, but only if this should happen during the winter.

             From these two points he argues as follows. Everything which happens either happens by chance or for the sake of an end. Now those things which happen outside the intention of an end are said to happen by chance. But it is impossible for those things which happen in every instance or in most instances to happen by chance. Therefore, those things which happen in every instance or in most instances happen for the sake of an end.

             Now whatever happens according to nature happens either in every instance or in most instances, as even they admitted. Therefore, whatever happens by nature happens for the sake of something.

             257. He gives the second argument where he says, 'Further, where a series . . .' (199 a 9). He says that there is an end for all things. That which is prior and all of its consequences are done for the sake of the end.

             Having assumed this he argues as follows. As something is done naturally, so is it disposed to be done. For 'so disposed' [aptum natum] means 'naturally'. And this proposition is convertible, because as something is disposed to be done, so it is done. However, it is necessary to add this condition: unless it is impeded.

             Therefore, let us agree that there is no impediment. Hence as something is done naturally, so is it disposed to be done. But things which happen naturally are done so that they lead to an end. Therefore, they are disposed to be done in such a way that they are for the sake of an end. And thus nature seeks an end, i.e., nature has a natural disposition for an end. Hence, it is clear that nature acts for the sake of an end.

             He clarifies what he has said by an example.

             One proceeds from the prior to the posterior in the same way in both art and nature. Thus if artificial things, e.g., houses, were made by nature, they would be made according to the order in which they now are made by art. Thus the foundation would be constructed first, and afterwards the walls would be erected, and finally the roof would be placed on top. For nature proceeds this way in the things which are rooted in the earth, i.e., in plants. Their roots, like a foundation, are fixed in the earth, the trunk, after the manner of a wall, is raised on high, and the branches are on top like a roof.

             And in like manner if the things which are produced by nature were made by art, they would be made according to the way they are disposed to be produced by nature. This is clear in regard to health, which happens to be produced by art and by nature. For as nature heals by heating and cooling, so also does art.

             Hence it is clear that in nature one thing is for the sake of another, i.e., the prior is for the sake of the posterior. And the same is true of art.

             258. He gives the third argument where he says, '. . . and generally art . . .' (199 a 16). He says that art makes certain things which nature cannot make, such as a house and things of this sort. However, in regard to those things which happen to be produced by art and by nature, art imitates nature, as is clear in regard to health, as was said above. Hence, if things which are made according to art are for the sake of an end, it is clear that things which are made according to nature also are made for an end, since in each case the prior and the posterior are similarly related.

             However, it can be said that this is not a different argument from the one already given, but is complementary to it and a clarification of it.

             259. He gives the fourth argument where he says, 'This is most obvious . . .' (199 a 20). This argument is drawn from those things in nature which more obviously seem to act for the sake of something.

             He says that it is most clear that nature acts for the sake of something when we consider animals which act neither through art, nor through inquiry, nor through deliberation. It is manifest in their operations that they act for the sake of something. Because of this some have wondered whether spiders and ants and animals of this sort act through intellect or through some other principle.

             But because they always act in the same way, it is clear that they do not act by intellect, but by nature. For every swallow makes a nest in the same way, and every spider a web in the same way, which would not be the case if they acted by intellect and from art. For not every builder makes a house in the same way, because the artisan judges the form of the thing built and can vary it.

             If we proceed beyond animals to plants, it is apparent among them that some things have been made and are useful for an end, as the leaves are useful as a covering for the fruit.

             Hence, if these things are due to nature and not to art, i.e., that the swallow makes a nest, and the spider a web, and the plants produce leaves for the sake of the fruit, and the roots of plants are not above, but below, so that they might take nourishment from the earth, it is clear that a final cause is found in things which come to be and are by nature, i.e., by nature acting for the sake of something.

             260. He gives the fifth argument where he says, 'And since nature means . . .' (199 a 30).

             He says that nature is used in two ways, i.e., for the matter and for the form. The form is the end of generation, as was said above. And the nature [ratio] of an end is that other things come to be for the sake of it. Hence it follows that to be and to come to be for the sake of something should be found in natural things.