For anything to be, Aristotle said, there must already exist a perfect example to be its cause. This poses the unanswered question where do these exemplars reside? Also, along the same line, Aristotle considered the most important cause of the existence of something to be its final cause, or the reason for its existence. This is called "Teleological reasoning" because it presupposes the reason for the existence of anything prior to the existence of the thing. In natural objects, he said, formal and efficient (or motive causes, whether natural or artificial are united in the same individual. For example the efficient cause of an animal is an animal, because it must be possessed of the form that will be realized in the offspring. On the other hand, that of a house is the builder but the form or design must already exist in his mind. The products of art have their form in the mind of the artist. He said that the formal, efficient, and final causes also tend to coalesce in one individual while the material is likely to be separate. Some causation is multiple, bronze and the sculpture are both necessary for the production of a statue. Bronze is matter and sphere is form but bronze is also the form of a compound with tin and copper being the materials. Underlying these is the four elements, hot, cold, earth and air out of which all materials are formed. Still beneath that he said, in a statement that relates back to Milesian cosmology, is a substratum that never exists alone but is the material from which the elements are formed. The elements can and do change one into another because they are constituted of this substratum that is common to them all.

However, if we follow this line of reasoning to its logical conclusion we find the ultimate assumption of the teleologist, that what underlies the existence of the universe must be an uncaused cause, and that it must be. That is, it must necessarily exist, in order that anything else can be. Movement and causation are used almost interchangeable in Aristotle's writings which makes sense if you assume that every change is a movement, and every movement must have a cause. This passage from Chapter 6, book XII of the Metaphysics explains why an eternal unmovable substance is necessary, that is, that its non-existence implies a contradiction.

Since there were three kinds of substance, two of them physical and one unmovable, regarding the latter we must assert that it is necessary that there should be an eternal unmovable substance. For substances are the first of existing things, and if they are all destructible, all things are destructible. But it is impossible that movement should either have come into being or cease to be (for it must always have existed), or that time should. For there could not be a before and an after if time did not exist. Movement also is continuous, then, in the sense in which time is; for time is either the same thing as movement or an attribute of movement. And there is no continuous movement except movement in place, and of this only that which is circular is continuous.

The Greeks assumed an eternal world that had no beginning and no end but which was always very much as it is. Yet a creation myth, a story of the beginning of the world is a part of the mythologies of all cultures. How can an eternal world be created or begun? In the Timaeus Plato said that when God created time he created both future and past. This made time both eternal and created. In a practical world of real things this makes little logical sense. Aristotle made a break with Plato here by stating that time must have been eternal. Also, in a relation that brings home his attatchment to existing things, he saw a relationship between time and movement. Remember that Aristotle was an Ionian grounded solidly in Ionian traditions. The source of all change and thus the source of all that is in Ionian tradition was eternal motion. But eternal motion must either turn back on itself or go on infinitely. It made more sense to Aristotle if it turned back on itself. Thus, eternal motion could only be in a circle. Remember that in the Timaeus Plato too said that perfect motion was necessarily in a circle, but for a different reason. Aristotle began by reasoning from actual experience.

But if there is something which is capable of moving things or acting on them, but is not actually doing so, there will not necessarily be movement; for that which has a potentiality need not exercise it.

But an eternal world cannot not be. Its existence is necessary. Even to think of the world as ever possibly not becoming in the sense that it may not have ever come into being makes no sense in an eternal world. The most important of the four Aristotelian causes was the last, the reason for the thing coming to be. Potentiality only becomes actuality with a purpose. That which is only potential not only need not, it will not become actuality without something additional, a reason for movement. Therefore, it is not sufficient that the action of the unmoved mover, that which began all motion, simply be possible, for it would still then require something else to give it a reason for causing motion and without that additional something there would be no existence.

Nothing, then, is gained even if we suppose eternal substances, as the believers in the forms do, unless there is to be in them some principle which can cause change; nay, even this is not enough, nor is another substance besides the forms enough, for if it is not, there will be no movement. Further, even if it acts, this will not be enough, if its essence is potency; for there will not be eternal movement, since that which is potentially may possibly not be. There must, then, be such a principle, whose very essence is actuality. further, then, these substances must be without matter; for they must be eternal, if anything is eternal. Therefore they must be actuality.

The underlying forces that created the universe according to the Milesians was eternal motion. But this implied something, for them the arche, that was in motion. It was not set in motion, it was always in motion. But the arche is nothing but the underlying substrata. It isn't anything. It just is. That is it is actual. For actuality is. It does not ever come to be. It has no need of cause. But for the Milesians the world was the result of strife among the opposites. It did not have a cause. There was no thought given to the possibility that the world was not necessary.

Yet there is a difficulty; for it is thought that everything that acts is able to act, but not everything able to act acts, so that the potency is prior. But if this so, nothing that is need be; for it is possible for all things to be capable of existing but not yet to exist.

More modern philosophers put it another way. They said that if anything exists then it is necessary that something exists. But since, as Aristotle said above, something being capable of existing does not insure that it will actually exist, either existence is a quirk of fate, an impossibility in any Aristotelian sense, or something must exist necessarily. This something must be unmoving and unchanging. This means it must be eternal and divine. As developed by Plato and Aristotle the eternal motion of the Milesians must of necessity turn back on itself in perfect circles, which is why Aristotle believed that everything that is has always been but is constantly regenerating itself. With this background we can continue into chapter 7 of book XII of the Metaphysics.

There is, then, something which is always moved with an unceasing motion, which is motion in a circle; and this is plain not in theory only, but in fact. Therefore the first heaven must be eternal. There is therefore also something which moves it. And since that which moves and is moved is intermediate, there is something which moves without being moved, being eternal, substance, and actuality. And the object of desire and the object of thought move this way; they move without being moved.

Desire and thought do not move, they exist already. They already contain actuality. Desire and thought, though seemingly unmoved are still caused by something else. Something prior.

The primary objects of desire and of thought are the same. for the apparent good is the object of appetite, and the real good is the primary object of rational wish. But desire is consequent on opinion rather than opinion on desire; for thinking is the starting point.

The idea that something is moved by desire while desire, being an object of thought is not moved, seems to be clear enough. However, desire is the result of thinking and not the other way around thus it cannot be that which originates movement. What is capable of originating movement must be the final cause of thought, the purpose for which thought is originated.

That a final cause may exist among unchangeable entities is shown by the distinction of its meanings. For the final cause is (a) some being for whose good an actions done, and (b) something at which the action aims; and of these the latter exists among unchangeable entities though the former does not. The final cause, then, produces motion as being loved, but all other things are moved by being moved.

Love provides the ultimate final cause for it moves but is not moved, it is always the final reason for which any action or thought is activated. It is the beginning of all movement.

Now if something is moved it is capable of being otherwise than it is. Therefore, if its actuality is the primary form of spatial motion, then in so far as it is subject to change, in this respect it is capable of being otherwise, --in place, even if not in substance. But since there is something which moves while itself unmoved, existing actually, this can in no way be otherwise than it is.

That something, love, exists which moves but is not moved has been proven. But could it be otherwise? It could not because if it did not exist then nothing would exist. It is pure love that produces the eternal movement of the heavens.

For motion in space is the first of the kinds of change, and motion in a circle is the first kind of spatial motion, and this the first mover produces. The first mover, then, exists of necessity; and in so far as it exists by necessity, its mode of being is good, and it is in this sense a first principle. for the necessary has all these senses--that which is necessary perforce because it is contrary to the natural impulse, that without which the good is impossible, and that which cannot be otherwise but can exist only in a single way.

On such a principle, Aristotle said the world of nature and all that we enjoy in it depend for their existence. It is a life that is the best that we can enjoy and yet for only a short while. For such a world may be eternal but we are not, but pleasure is the actuality of the eternal world. Thinking, on the other hand, deals with that which is best in itself.

If, then, God is always in that good state in which we sometimes are , this compels our wonder; and if in a better this compels it yet more. And God is in a better state. And life also belongs to God; for the actuality of thought is life, and God is that actuality; and God's self-dependent actuality is life most good and eternal. We say therefore that God is a living being, eternal, most good, so that life and duration continuous and eternal belong to God; for this is God.

Aristotelian science is derived from examining individual things and developing from those examinations inductive generalizations concerning the observations. It differs from modern science in that it does not include experimental manipulation of objects in order to develop additional insight. Some Aristotelian assumptions which were to be falsified in the sixteenth century AD were falsified through such experimentation. These included such assumptions as the idea that things tend to move toward where they belong. Thus, heavy objects belong on the ground and thus tend to move towards the ground while light things like fire belong in the heavens therefore tend to move up. We will discuss these problems again when we cover that period.

As you recall Plato's theory of knowledge and his theory of soul were intimately interrelated. An immortal soul was necessary as a messenger between the world of the forms and the world of the senses. Aristotle's theory of knowledge, dealing as it does with sensible objects, has no need of such an immortal soul. In De Anima, his treatise on Soul, his theory of soul was developed only after a long and complicated argument rejecting all of the ideas of his predecessors. This section, taken from Book II of De Anima , show the logical derivation of his concept of soul.

We are in the habit of recognizing, as one determinate kind of what is, substance, and that in several senses, (a) in the sense of matter or that which in itself is not 'a this', and (b) in the sense of form or essence, which is that, precisely in virtue of which a thing is called 'a this', and thirdly (c) in the sense of that which is compounded of both (a) and (b).

This use of purely general terms derived from his logical mind provides us the opportunity of witnessing the complete abstraction of essence from the existing. That something is, that we can talk about it, identify it. That it is something in itself, for that kind of being we use the term substance. But we use it in two senses, that something is, that is that we can name it, and that it is something, that we can identify what it is. The term substance can be used in either sense. That which exists in the sensible world is constructed of matter when we use the term matter as a general term for anything that is corporeal. Thus the term matter used alone in this way is nothing, but has the potentiality of being anything that can exist, that is it can be a substance in the sense that it is something that we can talk about. But, when we use the term matter we are not suggesting any particular thing. On the other hand since form is what makes a thing what it is, it is a substance in the other sense, it makes what has the potential of being anything a something that we can identify and talk about. Once form and matter have been conjoined then what it is conjoined as can not be anything other than that which it is. Finally, because Aristotle's use of the term substance is applied to anything we can talk about, we can use the term substance to indicate that which actually is, that which includes both the form and the matter and thus a something that exists.

Now matter is potentiality, form actuality; of the latter there are two grades related to one another as e.g. knowledge to the exercise of knowledge.

Among substances are by general consent reckoned bodies and especially natural bodies; for they are the principles of all other bodies. Of natural bodies some have life in them, others not; by life we mean self-nutrition and growth (with its correlative decay). It follows that every natural body which has life in it is a substance in the sense of a composite.

But since it is also a body of such and such a kind, viz, having life, the body cannot be soul; the body is the subject or matter, not what is attributed to it. Hence the soul must be a substance in the sense of the form of a natural body having life potentially within it. But substance (in the sense of form) is actuality, and thus soul is the actuality of a body as above characterized.

From long-standing Greek tradition the soul of a living thing is incorporeal, it does not include body. Yet it is, that is it exists in the sense that we can talk about it. Also, it is attributed to an existing thing yet is not an attribute of it, it does not modify what the thing is. It is thus equivalent to having knowledge rather than exercising knowledge. It also only applies to that specific entity. And this entity must have life. Consider the four causes and the implication, particularly of the final, that they have on what a thing is that is capable of movement on its own? What defines such a thing is its soul, that includes everything that makes it what it is including the quality by which it is capable of self-movement. Thus in such a body, soul is its form, that which when extracted from it represents the essence of the thing without being the thing, and as such is its actuality, but only in the sense that it is what it is and not in the sense that it is.

Now the word actuality has two senses corresponding respectively to the possession of knowledge and the actual exercise of knowledge. It is obvious that the soul is actuality in the first sense, viz, that of knowledge being possessed, for both sleeping and waking presuppose the existence of soul, and of these waking corresponds to actual knowing, sleeping to knowledge possessed but not employed, and, in the history of the individual, knowledge comes before its employment or exercise.

That is why the soul is the first grade of actuality of a natural body having life potentially in it.

That is why we can dismiss as unnecessary the question whether the soul and body are one; it is as meaningless to ask whether the wax and the shape given it by the stamp are one, or generally the matter of a thing and that of which it is the matter. Unity has many senses (as many as 'is' has), but the most proper and fundamental sense of both is the relation of an actuality to that of which it is the actuality.

That means that it is 'the essential whatness' of a body of the character just assigned. Suppose that what is literally an 'organ', like an axe, were a natural body, its 'essential whatness' would have been its essence, and so its soul; if this disappeared from it, it would have ceased to be an axe, except in name. As it is, it is just an axe; it wants the character which is required to make its whatness or formulable essence a soul; for that it would have had to be a natural body of a particular kind, viz, one having in itself the power of setting itself in movement and arresting itself. Next, apply this doctrine in the case of the parts of a living body. Suppose that the eye were an animalsight would have been its soul, for sight is the substance or essence of the eye which corresponds to the formula, the eye being merely the matter of seeing; when seeing is removed the eye is no longer an eye except for name--it is no more a real eye than the eye of a statue or of a painted figure.

As you can see his writing is not as clear as Plato's but it is more detailed. If soul is the form of a body in the sense that it is what makes a living thing what it is, then the soul cannot exist without the body, nor the body without the soul. Plato's immortal soul and his theory of knowledge were tied together. Neither could stand without the other. They are each substances because we can talk about them separately. But when we do this we extract them from the existing living thing. The soul in Plato's theory of knowledge was the messenger between the world of the forms and that of the senses. Now Aristotle has done away with the world of the forms and no longer has need of an immortal soul thus his theory of soul is very much in line with the assumption of particular things as the seat of reality. Therefore, in order to complete our understanding of Aristotle we need to understand his theory of knowledge and since this theory is based on his theory of mind we will turn to that next.