International Catholic University

Ancient Philosophy

Lesson Four: From Plato to Aristotle

1. Immanent essences

If the Platonic Ideas are required in order to have knowledge, knowledge of the things of this world is ambiguous. To know what the things of this world are, the mind must be directed to ideal entities, Forms or nature in virtue of which the things we sense are because they participate in those Ideas which are distinct from them. But if what things are is separate from them, to know what they are is to know something they are not.

We have seen the path by which Plato arrived at this odd position. The things of this world are hardly at all, constantly in change -- in the Theaetetus Plato basically accepts the Heraclitean view that sensible things are ever in flux. But knowledge in the strong sense requires something unchanging and necessary if it is to be necessary. The whatness of sensible things, unlike those sensible things themselves, is not subject to change. Aristotle of course accepts the Platonic condition of knowledge, above all necessity, but he came to hold that arguments against the Ideas or Forms -- that is, that the natures of the things around us exist separate and apart in an ideal world. It is not necessary, Aristotle held, to explain knowledge of sensible things by appeal to the Forms or Ideas.

Aristotle's basic charge against Plato is that he identified the way in which we understand with the way in which things are. If I know what daffodils are, the definition expressing it does not change and it is applicable to all daffodils past, present and to come. The characteristics of the nature as known are thus quite different from the characteristics of the things having that nature. But the next move, that the nature must be a separate entity, need not be made if it is the way in which we know the nature that gives it characteristics unlike those of the singular entities whose nature it is.

All our knowledge takes its rise in the senses, but sense perception of things provides a basis from which the mind abstracts the nature of singulars. As abstract, the nature is something one which relates to the many singulars. The abstract nature is thus universal in the sense that it is something one predicable of many. But the unity of the nature, the nature apart from the individuals, is a feature of our abstractive knowing. As something one over against the individuals it is something conceived by us. The nature does not exist apart from the individuals and it is something one only as abstracted by the human intellect. To assert that it exists apart, accordingly, is to confuse the status of the nature as known with the nature as it exists. It exists only in the individuals from which it has been abstracted. They are really similar to one another. In the case of living things, this similarity is established by the fact of generation. Parents have young like themselves, so different individuals. But the nature or similarity is not another existent individual. It is only when that real similarity is formulated in a concept that there is something one that relates to the many from which it has been abstracted.

This is not of course to say that the content of the concept is a mental construct, as if it did not express what is found individually in members of a species, say. But as expressed, it leaves out what belongs to individuals as individuals -- that is what abstracting means. Doubtless it was the relation of cause and effect, generator and generated, parent and young, among the individuals that motivated Aristotle in resisting the notion that appeal had to be made to some beyond in order to explain that similarity. That offspring are really like their parents is a given and when the likeness is isolated by the mind in thinking of the individuals, a nature that exists only in those individuals is considered apart but must not be asserted to exist apart.

This is difficult matter, of course, and we shall return to it. But in order to see the transition from Plato to Aristotle it is well to begin with what Aristotle considered to be his principal difference from his master. Plato, as we have stressed, was aware of the difficulties that confronted the doctrine of Ideas, but these difficulties prompted him to seek a defensible account of the Ideas. Aristotle, having learned those difficulties in the Academy, came to see an alternative to them. And this opened the door to a science of natural things as such.

2. Natural philosophy

Our earlier discussion of Parmenides provided us an opportunity to present Aristotle's resolution of the problems Parmenides had put in the way of a science of nature. Plato may be thought of us as developing a modified form of the Parmenidiean notion that sense perception is deceptive, giving us a world of appearance that must be contrasted with what really is. Aristotle rejects, for reasons we have given, both the Parmendiean contrast between appearance and reality and the Platonic modification of it.

The Physics is the first in a series of works that Aristotle devoted to natural science. How is it first? Aristotle observes that our knowledge proceeds from general more or less confused knowledge to specific and distinct knowledge. He provides this example. You see something afar off and it is just something. As you approach it, or as it approaches you, you discern that it is moving itself and not just being blown along. The living thing is then seen to be two-footed and then a human male. Too late you see that it is one of your creditors. Aristotle sees here the pattern of our knowledge. We begin with generic truths about the things we sense and proceed to more specific knowledge of them.

Notice that it is the approaching object, something you are sensing, that is grasped under progressively more discriminating concepts. If we should, following Porphyry, see a kind of ladder here, the top rung of which would be substance, the next rung living / non-living, the next having senses / not having senses, the next having reason / not having reason, we would not think that we are knowing a series of things, but knowing a thing with progressively more determination or discrimination. On the Theory of Ideas, these levels of knowing would be taken to answer to levels of reality, a hierarchy of being. But there is no substance that is not either animate or inanimate, no animate thing that is neither animal or not, no animal that is either rational or not. This is our way of knowing things, not the way in which things exist.

So it is that in our pursuit of a science of nature, we will first seek truths which are common to all natural things and then go on to pursue knowledge of what is peculiar to living things. The assumption is that what has first been established will apply to living things, but not as living things, since it will also apply to the inorganic.

We can now place in this schema the analysis of change and the product of change that we sketched earlier in discussing Aristotle's response to Parmenides. A particular example of a change is analyzed to find the most general truths about change and the most general description of something that comes about as the result of a change, that is, a physical object, a natural thing. To establish that change involves a subject and contrary states of that subject and that the result of a change is a subject plus a new characteristic is to establish a truth of sweeping generality. It is not a specific statement about any kind of change or product of change. It is the first thing that can be said of any change. The eight books of the Physics contain truths about physical things at a similar level of generality. The discussions of motion, time and place and the argument that all movers cannot be moved movers, that there must be a first unmoved mover, indicates the importance of the truths that can be thus gained.

3. First philosophy

If the study of the natural world comes first, it does not deal with things which are first. Like Plato, Aristotle assumes that philosophy can attain knowledge of the divine, eternal and unchangeable, but it cannot attain such knowledge in the way Plato attempted to. The pedagogical assumption of Aristotelian philosophy is that we begin with a science of natural things, of things which can be grasped by the senses, because these are unproblematic for us. That there is change and a plurality of changing things is an assumption that is not proved, though its denial can be refuted. What cannot be taken as an unproblematic assumption is that there are existent things beyond or apart from natural things. Mathematics deals with things whose definitions make no reference to matter or change, but mathematicals do not exist in the way in which natural things exist. They are idealizations of aspects of natural things. If there is to be knowledge of immaterial things, we have to prove that there is something to know. This breakthrough is made in the course of natural science.

The prime mover.

The distinction between the potential and the actual emerges from the analysis of change. A subject that does not have a given characteristic and subsequently has it may be said to move from a state of potentiality with regard to that characteristic to one of actuality, that is, of actually having it. When Aristotle defines motion as "the act of a being in potency insofar as it is in potency" he is seeking to express a subject's being actualized. Take as an example a ball that moves from A to B. How express its movement. At A it is not at B but can be, that is, is potentially at B. When it is in movement it can be said to have actualized the potentiality to be at B but, since it has not yet arrived there, to be still in potentiality. If it stopped, it would actually be at some point between A and B. As moving, it continues to actualize its potentiality to be at B. Aristotle's definition, as stated above, by using act and potency, defines motion without putting some synonym of motion into the definition (as I have in explicating the definition).

Motion, so defined, is the act of a thing that is being moved. The ball must be started on its way by something else, a mover. Of course the mover itself may be moved by some third thing. And so forth. There could not be a series of related moved movers that went on indefinitely, since then, instead of explaining why the motion we began with is taking place, we would simply be putting off an explanation of it. An infinite series is not an explanation but the failure to explain. There cannot be an infinite series of moved movers. From this it follows that the series must be explained by an unmoved mover, a mover whose moving of other things is not explained by its being moved.

Because of what is entailed by being a moved mover, the unmoved mover emerges as something immaterial. I am merely asserting what is shown to be the case in the Physics because what I am concerned to show is that this proof is a basis on which it can be said that to be and to be material are not identical, and this is a conclusion that is reached in the course of doing natural science. But if natural science is concerned with material things, it cannot be the science that deals with immaterial things. So another science, and not mathematics, must deal with things that exist apart from matter.

The immortality of the soul.

When Aristotle begins his study of living substances, he begins with a short work devoted to that principle in living things which distinguishes them from non-living things, namely, the soul. On the Soul will thus speak of this principle as the form of living things. Having defined soul, it will discuss the various vital activities, sense perception, the internal senses, and then take up the question of intellection. The activity of sensation rides piggy-back upon a physical change. That is, when I touch something, its temperature affects my hand, and vice versa. But this physical change is a condition of touch not touch as such, since then any warmed body would be said to feel heat. Intellection is distinguished from sense perception because it does not intrinsically involve a physical change. Coming to understand what an acorn is does not involve a physical change the way feeling or seeing or hearing or tasting or smelling an acorn does. Intellection is thus seen to be an immaterial process and the soul capable of such activity is seen itself to be capable of existing apart from matter. The argument for this is far more complicated than this sketch indicates, but again what I am chiefly concerned with now is the way in which another argument within natural science concludes to the existence of something apart from matter.

The science of being as being.

Against this background -- that we can know there are immaterial beings and that mathematics does not deal with things which exist apart from matter -- the need for a science beyond natural science and mathematics is clear. Aristotle's development of this science is found in the work called the Metaphysics, which is not what Aristotle himself called it. He called it wisdom -- that is the goal toward which the philosophical quest tends -- first philosophy, as dealing with things which are prior to natural things; theology, as dealing with the divine and changeless and eternal. In the Metaphysics it is also often designated as "the science we are seeking" or by references to its subject matter, "the science of being as being."

Natural science deals with being as changeable; mathematics with being as quantified. The science we are seeking is not concerned with a type or kind of being, but with being as being. Why? If the pursuit of this science is generated by proofs that there things which exist apart from matter, why not call it the science of a kind of being, namely, immaterial being? Because the dependence of our knowledge of the immaterial on our knowledge of the material does not go away when we begin to construct this new science. In order to establish what belongs to being as such, we must consult again and again the kind of being easily accessible to us, natural or physical being.

But why not, on the basis of what was said about the human mode of knowing, why not say that being is the most general term of all, prior to subject since it is predicable of accidents as well as substance, so we can simply ask about the characteristics of being in general and apply it to immaterial beings?

Being as it is first known is inadequate to give any information about immaterial being. If by being we mean "that which exists", the applicability of this to any non-material being is totally uninformative unless we know what "that which" might mean in immaterial things, and consequently what "exists" means in their case.

Aristotle's first move is to point out that "being" is not a genus and thus is not predicated univocally of the things that are. A man and his complexion do not exist in the same sense though they both can be counted among the things that are. The comparison with "healthy" is offered, a term which is said of many things, but with different meanings. As "being" can be rendered "that which exists", so "healthy" can be rendered "that which has health." But an animal has health differently than his diet and urine do, yet we say of all three that they are healthy. It is because we must refer to the health of the animal to grasp the meaning of healthy as said of food and urine that we recognize a primary and controlling sense of the term. In the case of being, that which has existence in the primary and controlling sense of the term is substance. Thus the science of being as being, can concentrate on substance.

The word 'substance' is applied, if not in more senses, still at least to four main objects; for both the essence and the universal and the genus are thought to be the substance of each thing and fourthly the substratum. (Metaphysics 7,3)

As Thomas Aquinas points out in his commentary (lectio 2, n. 1275), it is well to think of this division by comparison with the Categories where substance is said to be of two kinds, first substance, that is the individual substance, and second substance, that is, the universal. In the passage just quoted, 'universal' and 'genus' match second substance and the substratum, that is, this thing, first substance. The new element then is essence. "There (in the Categories) the what-a-thing-is (essence) is omitted because it does not belong to the order of categories except as their principle. For it is neither a genus nor species nor an individual, but the formal principle of all these." Thus the task before him is seen: we must ask after the individual substance and its essence.

What can surprise, given the fact that we are looking for a science whose subject is not a kind of being, is the immediate turning to material substance in order to grasp the understanding of the relation between essence and individual. To make a long and intriguing story short, reflection on material substance, which is composed of matter and form, makes clear that form is the most important element, that which in the material substance most makes it to be a substance. This is established by a series of painstaking analyses, with the upshot that we can say that if substance is to be applied to a non-material substance, we can understanding it as a subsisting form.

Obviously this analogous sense of substance is not common to material and immaterial substance -- the latter cannot be called a subsisting form even though its form is that which is most substance in it. What this analysis shows is the way an analysis of the kind of being most accessible to us, material being, is the basis on which extrapolation is made to the immaterial. Immaterial beings are not given to us immediately as are material substances. We require truths about material substances in order to demonstrate that there are immaterial substances. And we need analyses of material substance to ground any and every assertion about immaterial substance. It is this which makes metaphysics so difficult and oblique a science. When in Book Twelve, Aristotle speaks of God as "thought thinking itself," his statement depends upon an understanding of human intellection and the extrapolation from it of what can be asserted of the activity of a non-material substance. So it is that the Metaphysics culminates in such knowledge of the divine as we can acquire and receives the title theology.

Writing assignment: Write briefly on one of the following:

1. What account of human knowledge lies behind putting the Physics first in natural science?

2. Compare and contrast natural philosophy, mathematics and metaphysics.

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