LECTURE 11 (198 a 22-b 9)

NATURAL PHILOSOPHY DEMONSTRATES FROM ALL OF THE FOUR GENERA OF CAUSES

             241. Having treated the causes, the Philosopher here shows that the natural philosopher demonstrates from all the causes.

             Concerning this he makes two points. First he states his intention. Secondly, where he says, 'The last three . . .' (198 a 25), he explains his position.

             He says, therefore, first that inasmuch as there are four causes, as was said above, it pertains to natural science both to know all of them and to demonstrate naturally through all of them by reducing the question 'why' to each of the aforementioned causes, i.e., the form, the moving cause, the end and the matter.

             Next where he says, 'The last three . . .' (198 a 25), he explains his position. Concerning this he makes two points.

             First he sets forth certain things which are necessary to clarify his position. Secondly, where he says, 'The question . . .' (198 a 32), he proves his position.

             Concerning the first point he sets forth two things which are necessary for the proof of what follows. The first of these deals with the relationship of the causes among themselves. The second deals with the consideration of natural philosophy, and is given where he says '. . . and so too in general . . .' (198 a 27).

             242. He says, therefore, first that it often happens that three of the causes combine into one, such that the formal cause and the final cause are one in number.

             This must be understood to apply to the final cause of generation, not, however, to the final cause of the thing generated. For the end of the generation of man is the human form, but this form is not the end of man. Rather through this form man acts for his end.

             But the moving cause is the same as both of these according to species. And this is especially true in univocal agents in which the agent produces something like unto itself according to species, as man generates man. For in these cases the form of the generator, which is the principle of generation, is the same in species as the form of the generated, which is the end of the generation. However in non-univocal agents the species [ratio] is different. For in these cases the things which come to be cannot reach the point where they follow upon the form of the generator according to the same kind [ratio] of species. Rather they participate in some likeness to it, insofar as they are able, as is clear in those things which are generated by the sun. Therefore, the agent is not always the same in species with the form which is the end of generation, and furthermore, not every end is a form. And because of this it is significant that he said 'often'.

             The matter, however, is neither the same in species nor the same in number as the other causes. For matter as such is being in potency, whereas the agent as such is being in act, and the form or the end is act or perfection.

             243. Next where he says, '. . . and so too . . .' (198 a 27), he makes his second point which deals with the things which natural philosophy should treat.

             He says that it pertains to natural philosophy to consider any movers which move in such a way that they are moved. Things, however, which move, but are not themselves moved, do not belong within the consideration of natural philosophy which properly considers natural things which have in themselves a principle of motion. For movers which are not themselves moved do not have in themselves a principle of motion, since they are not moved but are immobile. Thus, they are not natural things, and as a result do not come under the consideration of natural philosophy.

             Hence, it is clear that there are three branches of study, i.e., the study and intention of philosophy is threefold according to the three genera of things which are found.

             For some things are immobile, and one philosophical study deals with them. Another philosophical study deals with things which are mobile but incorruptible, such as the celestial bodies. And there is a third philosophical study which deals with things which are mobile and corruptible, such as the inferior bodies.

             The first of these studies pertains to metaphysics, while the other two pertain to natural science which treats all mobile things, both corruptible and incorruptible.

             Hence some have misunderstood this passage, desiring to reduce these three studies to the three parts of philosophy, namely, mathematics, metaphysics and physics. For astronomy, which seems to consider the incorruptible mobile things, belongs more to natural philosophy than to mathematics, as was said above. For insofar as it applies mathematical principles to natural matter, it considers mobile things. Therefore, this division is taken according to the diversity of things existing outside the mind and not according to the division of the sciences.

             244. Next where he says, 'The question "why" . . .' (198 a 32), he sets forth his position.

             Concerning this he makes two points. First he shows that it pertains to natural philosophy to consider all the causes and to demonstrate through them. These are the two points he has proposed above. Secondly, where he says, 'We must explain . . .' (198 b 10), he proves certain things which are assumed in this argument.

             Concerning the first part he makes two points. First he shows that natural philosophy considers all the causes. Secondly, where he says, 'We must explain . . .' (198 b 4), he shows that it demonstrates through all of them.

             Concerning the first part he makes two points. First he shows that natural philosophy considers the matter and the form and the moving cause. Secondly, where he says, '. . . the essence of that . . .' (198 b 3), he shows that it considers the end.

             Concerning the first part he makes two points. First he states his intention, and secondly, he proves it, where he says, 'For in respect of . . .' (198 a 33).

             First he concludes from what was said above that the 'why' is assigned to natural things by reference to the matter, and to what the thing is, i.e., the form, and to the first mover.

             245. Next where he says, 'For in respect of . . .' (198 a 33), he proves his position as follows.

             It has been said that natural philosophy considers those things which are moved, both the generable and the corruptible. Therefore, whatever should be considered about generation should be considered by natural philosophy. But with reference to generation one ought to consider the form, the matter, and the moving cause.

             Those who wish to consider the causes of generation consider them as follows. First we consider what it is that comes to be after something, as fire come to be after air, since fire is generated from air. And in this way the form, through which the generated is what it is, is considered.

             Next we consider what it is that first makes [this], that is, we consider that which first moves to generation. And this is the moving cause.

             Next we consider what it is that undergoes this change. And this is the subject and the matter.

             With reference to generation we consider not only the first mover and the first subject, but also those things which are consequent upon them. And thus it is clear that it pertains to natural philosophy to consider the form, the mover, and the matter.

             However, natural philosophy does not consider every mover. For there are two kinds of moving principles, namely, the moved and the non-moved. Now a mover that is not moved is not natural, because it does not have in itself a principle of motion. And such is the moving principle which is altogether immobile and the first of all movers, as will be shown in Book VIII.

             246. Next where he says, '. . . the essence of that which . . .' (198 b 3), he shows that natural philosophy also considers the end.

             He says that the form and what the thing is also fall under the consideration of natural philosophy, insofar as the end is that for the sake of which the generation occurs. For it was said above that the form and the end coincide in the same thing. And since nature acts for the sake of something, as will be proven below, it must belong to natural philosophy to consider the form not only insofar as it is form but also insofar as it is the end. If, however, nature were not to act for the sake of something, then natural philosophy would consider form insofar as it is form, but not insofar as it is an end.

             247. Next where he says, 'We must explain . . .' (198 b 4), he shows how natural philosophy demonstrates through all the causes.

             First he shows how it demonstrates through matter and the moving cause, which are the prior causes in generation. Secondly, where he says, '. . . that this must be so . . .' (198 b 7), he shows how it demonstrates through the form. Thirdly, where he says, '. . . because it is better . . .' (198 b 8), he shows how it demonstrates through the end.

             He says, therefore, first that in natural things the 'why' must be elaborated fully, i.e., in every genus of cause. Thus if something has gone before, whether it be the matter or the mover, then something necessarily follows. For example, if something is generated from contraries, it is necessary that the latter be corrupted, and if the sun approaches the north pole, the days must become longer, and cold must diminish and heat increase for those who dwell in the northern part.

             However, we must realize that it is not always necessary that something follows from a preceding matter or mover. Rather sometimes a thing follows simply or in every case, as in the things mentioned. But sometimes a thing follows in most instances, e.g., from human seed and a mover in generation, it follows in most instances that what is generated has two eyes, but at times this fails to happen. Similarly, because of the fact that matter is so disposed in the human body, it happens that a fever is frequently produced because of festering, but at times this is impeded.

             248. Next where he says, '. . . that this must be so . . .' (198 b 7), he shows how in natural things demonstration must be made through the formal cause.

             In order to understand this, we must know that when something follows from the preceding causes in generation (i.e., from the matter and the mover) by necessity, then a demonstration can be established, as was said above. However, a demonstration cannot be established when something follows in most instances. But then a demonstration should be founded upon that which is posterior in generation in order that something might follow of necessity from another, just as the conclusion follows from the propositions of a demonstration. Thus let us proceed in demonstration as follows: if this should come to be, then this and that are required, for example, if man should be generated, it is necessary that human seed be an agent in the generation.

             If, however, we proceed conversely by saying that 'human seed is an agent in generation', then the proposition 'therefore man will be generated', does not follow as a conclusion follows from propositions. But that which ought to come to be, i.e., that in which the generation is terminated, was (as was said above 'what the thing was to be', i.e., the form.

             Hence, it is clear that when we demonstrate according to this mode, i.e., 'that "this must be so if that is to be so" ' (198 b 7), we demonstrate through the formal cause.

             249. Next where he says, '. . . because it is better . . .' (198 b 8), he shows how natural philosophy demonstrates through the final cause.

             He says that natural philosophy sometimes also demonstrates that something is true because it is better that it be so. For example, we might demonstrate that the front teeth are sharp because as such they are better for cutting food, and nature does what is better. Nature does not, however, do what is better simply, but what is better with reference to what belongs to each substance; otherwise nature would give a rational soul, which is better than an irrational soul, to each animal.