This argument set the stage for the next, or the opening of Plato's theory of knowledge as recollection and his theory of forms. You should be able to see that up to this time he has essentially unified the Hericlitean doctrines of opposites and change and the Pythagorean doctrine of the transmigration of souls. His next step, in a truly master stroke, is to further unify the doctrines of Hericlitus and Parmenides to show that it is possible for there to be both pure unchanging entities which he calls the forms, and the constantly changing things of the sensual world. Of course we can only have knowledge of the unchanging therefore he must and does explain how we gain that knowledge. By the same token if we cannot have knowledge of constantly changing things then what of our experience of them and from where do they gain their characteristics?

In the Phaedo Cebes brought up Socrates doctrine that knowledge is simply recollection. If it is true, it also necessarily implies a previous time in which we have learned that which we now recollect. "But this would be impossible," he said, " unless our soul had been in some place before existing in the form of man; here then is another proof of the soul's immortality." One proof, that he offered referred back the discussion in the Meno. If you put a question to a person in the right way, he will give a true answer of himself, an answer he could not give unless there were knowledge and right reason already in him?

This problem is more important than it appears to be. Plato does not need to get into detail about it because the doctrine of recollection insures that the basic substance of everyone's knowledge is the same and therefore people can exchange ideas about things that all are acquainted with even though they may have different opinions concerning them. When you get away from the concept of platonic forms then you are faced with the problem of consistent knowledge among people of differing backgrounds. Aristotle's approach to mind required the existence of a class of thinkable things which people could share in equally. The first to offer an answer to this problem without resorting to something approaching platonic forms was John Locke. He said that the ideas in each man's mind were private, but men communicate using words determined to express those ideas but which were developed through arbitrary agreement. Men cannot share in each others thoughts and must develop their own expressions of them by communicating with others. This involves a very complicated process and most modern philosophers still have failed to understand exactly what Locke had in mind. However, we should take a closer look at Plato's doctrine of recollection.

But if, said Socrates, you are still incredulous, Simmias, I would ask you whether you may not agree with me when you look at the matter in another way;--I mean, if you are still incredulous as to whether knowledge is recollection?

Incredulous I am not, said Simmias; but I want to have this doctrine of recollection brought to my own recollection, and, from what Cebes has said, I am beginning to recollect and be convinced: but I should still like to hear what you were going to say.

This is what I would say, he (Socrates) replied,We should agree, if I am not mistaken, that what a man recollects he must have known at some previous time.

And what is the nature of this knowledge of recollection? I mean to ask, whether a person who, having seen or heard or in any way perceived anything, knows not only that, but has a conception of something else which is the subject, not of the same but of some other kind of knowledge, may not be fairly said to recollect that of which he has the conception?

The doctrine of recollection does not require that one experience exactly the same thing in order to be reminded of it. It only requires that there be some connection between what is experienced and what is recollected. You may be reminded of a friend you once knew who liked to pitch when you played baseball and later when you see someone using a similar wind-up routine, you are reminded of him.

I mean what I may illustrate by the following instance: the knowledge of a lyre is not the same as the knowledge of a man?

And yet what is the feeling of lovers when they recognize a lyre, or a garment, or anything else which the beloved has been in the habit of using? Do not they, from knowing the lyre, form in the mind's eye an image of the youth to whom the lyre belongs? And this is recollection. In like manner, anyone who sees Simmias may remember Cebes (his brother); and there are endless examples of the same thing.

And recollection is most commonly a process of recovering that which has been already forgotten through time and inattention.

Well; and may you not also from seeing a picture of a horse or a lyre remember a man? and from a picture of Simmias, you may be led to remember Cebes?

Simmias and Cebes are brothers. Family resemblances are one sort of trigger for recollection. It isn't even necessary that you have ever met Simmias to have a recollection of Cebes when you see his brother's picture.

Or you may also be led to the recollection of Simmias himself? And in all these cases, the recollection may be derived from things either like or unlike?

And when the recollection is derived from like things, then another consideration is sure to arise, which is--whether the likeness in any degree falls short or not of that which is recollected?

When we are reminded of something by something that is like it, that likeness is never perfect. It is always a similarity, not an identity. In fact we never experience two things that are completely identical. There is always something, even though it might be ever so slight, that makes one of them different from the other.

And shall we proceed a step further, and affirm that there is such a thing as equality, not of one piece of wood or stone with another, but that, over and above this, there is an absolute equality?

And do we know the nature of this absolute essence?

And whence did we attain our knowledge? Did we not see equalities of material things, such as pieces of wood and stones, and gather from them the idea of an equality which is different from them? for you will acknowledge that there is a difference. Or look at the matter in another way:--Do not the same pieces of wood appear at one time equal and at another time unequal?

But are real equals ever unequal? or is the idea of equality the same as of inequality?

Then these (so-called) equals are not the same with the idea of equality?

And yet from these equals, although differing from the idea of equality, you conceived and attained that idea?

But that makes no difference: whenever from seeing one thing you conceived another, whether like or unlike, there must surely have been an act of recollection?

But what would you say of equal portions of wood and stone or other material equals? And what is the impression produced by them? Are they equals in the same sense in which absolute equality is equal? or do they fall short of this perfect equality in a measure?

This problem occurs whenever we discuss absolute essences, or perfection in general. Whenever we compare two things, saying one is better or worse than another we are grading them on a scale. But in life we never experience the limit of that scale. We may say that two stones are equal but we seldom really mean it. We mean that for the purpose in mind they are equivalent. If we have never experienced perfect equality, or perfect beauty, or the maximum of any other scale we might judge something by, then how can we make comparisons.

And must we not allow, that when I or any one, looking at any object, observes that the thing which he sees aims at being some other thing, but falls short of, and cannot be, that other thing, but is inferior, he who makes this observation must have had previous knowledge of that to which the other, although similar, was inferior?

And has not this been our own case in the matter of absolute equality?

Then we must have known equality previous to the time when we first saw the material equals, and reflected that all these apparent equals strive to attain absolute equality, but fall short of it?

And we recognize also that this absolute equality has only been known and can only be known, through the medium of sight and touch, or some other of the senses, which are all alike in this respect?

From the senses then is derived the knowledge that all sensible things aim at an absolute equality of which they fall short?

Then before we began to see or hear or perceive in any way, we must have had a knowledge of absolute equality, or we could not have referred to that standard the equals which are derived from the senses?--for to that they all aspire, and of that they fall short.

Notice that this is an absolute. We have never experienced anything that was perfectly equal, or for that matter perfect in any way the mind can imagine.

And did we not see and hear and have the use of our other senses as soon as we were born?

Then we must have acquired the knowledge of equality at some previous time?

That is to say, before we were born.

And if we acquired this knowledge before we were born and were born having the use of it, then we also knew before we were born and at the instant of birth not only the equal or the greater or the less, but all other ideas; for we are not speaking only of equality, but of beauty, justice, holiness, and of all which we stamp with the name of essence in the dialectical process, both when we ask and when we answer questions. Of all this we may certainly affirm that we acquired the knowledge before birth.

But if after acquired, we have not forgotten what in each case we acquired, then we must always have come into life having knowledge, and shall always continue to know as long as life lasts--for knowing is the acquiring and retaining of knowledge and not forgetting. Is not forgetting, Simmias, just the losing of knowledge?

But if the knowledge which we acquired before birth was lost by us at birth, and if afterwards by the use of the senses we recovered what we previously knew, will not the process we call learning be a recovering of the knowledge which was natural to us, and may not this be rightly termed recollection?

Plato's theory of forms overcame some of the problems of both Hericlitus and Parmenides through the application of Pythagorean principles. Everything that can ever exist in the sensible world has a perfect form in the world of the forms. However, what exists in the sensible world is constantly changing. We can never have knowledge of what is constantly changing because as soon as we have knowledge of it, it changes to something else. The forms, on the other hand, are permanent, they never change. The world they exist in is the world of the eternal, the blessed world where nothing ever changes. But Parmenides made the point that if nothing changes then there can not be many things since then there would necessarily be a separation between them and this separation would be something that was not and it is impossible for there to be and not to be at the same time. Plato's world of forms does not have that kind of existence. Because the world of the true forms does not have existence, it has reality, it is a real world separate from the sensible. At the same time, there can be many things in the sensible world because they attain their existence by participating in the perfect forms. In other words a single thing can participate in both the beautiful and the ugly and thus have a range of beauty in which to change. By the same token one can participate in tallness by being taller than another and in shortness by being shorter than a third person. However, as you can see, his theory of forms is intimately bound up with his belief in the immortality of the soul. Not only, as many moderns do, that the soul exists after the death of the body, but as well that it existed prior to the birth of the body. This naturally leads to a special kind of doctrine of transmigration of souls where the soul after death and before rebirth exists in this world of the pure forms and gains all of its knowledge there. As we shall see, these doctrines had a great deal to do with the development of our western heritage.

In the Parmenides Plato depicted a young Socrates arguing the basics of his theory of forms with an elder Parmenides. Its purpose was to bring out the differences between his idea of the forms and that of the Eleatic one. Plato's profound respect for the Eleatic master is obvious throughout the dialogue. The theory of the one being Plato felt was a major undertaking in philosophy. But it is the transcendental reality of the soul as the messenger between the world of the forms and the sensible world that allowed Plato's approach to extend philosophy into the moral world. Here are some of the arguments provided by Parmenides against the Existence of the Forms.

1. Socrates theory of the forms separated the forms from the things that shared in them. Therefore there exists a "similarity itself" separate from the similarity that we recognize. This entails an unlimited scope but Socrates was not ready to concede this. When it came to things like beautiful and just he found no problem, when it came to natural substances like fish he hesitated, and when it came to worthless things like hair, clay and dirt, he said that would be absurd. He shied away from it by returning the conversation to things he was sure of, like the moral and mathematical forms.

2. Parmenides said that if a form must be divisible then each large thing will be large by having a portion of largeness smaller than largeness itself. If the explanation of a man being small is that he possess a part of smallness then the smallness must be larger then the small itself and a man will be made smaller by having something added.

3. The Third Man Argument is an extension of the one over many argument. The one over many argument shows that for every particular instance there must be one form. For every particular flesh and blood man there is a form that is called men. But, to account for the fact that the form of men correctly accounts for the form of man there must be a third form of man. The argument evolves into an infinite regress.

4. Parmenides said that if other things partake of the forms then either each will be composed of thoughts and thus everything would think, or else they are unthinking thoughts. Is it a thought that thinks or a mind that forms it? When we think of something existing outside us there are three factors involved: a thinking mind, the concept which it forms, and the reality of which it is a concept. But this only applies to the idea that the forms are no more than concepts in the mind, an idea that Plato rejected anyway.

5. The meaning of participation, Parmenides said, is that the forms are the patterns fixed in the real world and particulars resemble them and are fixed in the sensible world. He said that this relationship must be reciprocal: as the particular resembles the form so the form must resemble the particular. If two things resemble each other they share the same character and that character is another form. Thus for anything to resemble a form would require a second form and that would lead to an infinite regress. Plato did not answer this objection in the Parmenides. He did provide an answer in the Cratylus where he stressed the point that the forms are intelligible and thus could never be on a par with the sensible.

6. Parmenides said that the forms, if they exist by themselves in their own world, they must be related only to each other, not to copies in the sensible world. At the same time things in the sensible world, though named after the forms, could only be related to each other. Since knowledge implies necessary knowledge of something, then knowledge will have as its objects varieties of reality. Therefore if we have no part of the forms which are not in our world, then we can have no knowledge of the forms and if any being has it, it must be a god and knowledge in the world of the gods cannot be knowledge to us. What is missing in Parmenides conception here is the relationship of the soul as the epistemological link between the sensible world and the world of the forms.

In the Theatetus Plato tackled those problems that Parmenides saw in the relationship between his theory of knowledge and his theory of forms. These arguments were brought forward to prove that everything that is conceivable can be put into one of two categories, the sensible and the intelligible. The intelligible is eternal, invisible and wholly real, the realm of being. The sensible, including the entire world and everything in it, is the realm of becoming.

The statement that Theatetus made was that knowledge is nothing but perception, whoever knows something is perceiving it. Socrates said that the statement was the same as Protagoras' most famous statement, that man is the measure of all things, of what is that it is, of what is not that it is not. What Plato said this meant was that since everything that exists for the individual is exactly what he perceives it to be then man's perception is infallible. He can never be wrong. The sensible world of Protagoras is a world of becoming. The sensations of each person then become what they are individual to that person. Why then should Protagoras be the teacher, Socrates asked? If each person is the measure of his own wisdom then why should one person's knowledge be better than another's. To attempt to refute the notions and opinions of others would be sheer folly. Plato's answer was that truth is real truth and the philosopher is not merely amusing himself by giving oracles out of the shrine of his book. The power which discerns not only in sensible things but in all things those universal notions which we call being and not-being is the mind. The mind has a power of its own that contemplates the universals in all things.

Socrates used three axioms to dispute the Protogorean approach to knowledge.

1. Nothing can become greater or less, either in number or magnitude while remaining equal to itself.

2. Without addition or subtraction their is no increase or diminution, only equality.

3. What was not before cannot be afterwards without having become.

Since Socrates, a grown adult is taller than Theatetus, a growing young man, in time the boy will outgrown the man. In that way Socrates would become something different, he would then be smaller than Theatetus without anything having been subtracted and without his having become something different. He showed that they couldn't even be sure they were not dreaming. Therefore, Protagoras as well as the idea that knowledge is perception is incorrect, everything is in constant motion. Even the act of sensation itself is motion. Not only that but a man may have real knowledge and still not possess it. Knowledge may very well be true opinion, but though man may have true opinion he may mistake what it is he applies this opinion to. Thus a man may be mistaken even though he has knowledge.

If knowledge is only of the universals that are explicit in individual things, then knowledge can only be of non-material things. As has been said before, one can not have knowledge of individual things because they are under constant change and knowledge can only be of what does not change. Plato is one of the earliest idealists, that class of philosophers who believe that what is real can only be understood through the mind. What we experience, the changing world of the senses, is an illusion. In the Sophist Plato used the ancient conflict between the Titans and the Gods from Hesiod as a mechanism for describing the battle between materialism and idealism. The dialogue is between Theatetus and an Eleatic stranger. In these later dialogues Socrates either becomes a minor character, or disappears entirely.

Stranger. There appears to be a sort of war of giants and gods going on amongst them; they are fighting with one another about the nature of essence.

Theatetus. How is that?

Stranger. Some of them are dragging down all things from heaven and from the unseen to the earth, and they literally grasp in their hands rocks and oaks; of these they lay hold, and obstinately maintain that the things only which can be touched or handled have being or essence, because they define being and body as one, and if any one else says that what is not a body exists they altogether despise him, and will hear of nothing but body.

Theatetus. I have often met with such men, and terrible fellows they are.

Stranger. And that is the reason why their opponents cautiously defend themselves from above, out of an unseen world, mightily contending that true essence consists of certain intelligible and incorporeal forms; the bodies of the materialists, which by them are maintained to be the very truth, they break up into little bits by their arguments, and affirm them to be, not essence, but generation and motion. Between these two armies, Theatetus, there is always an endless conflict raging concerning these matters.

Materialists, however, would freely admit to their being a mortal animal. They all admit that their exists a body with a soul. Since one soul may be wise and another foolish, they both must possess something, in this case wisdom and foolishness, that is immaterial. Therefore what they possess must exist. If both the virtues and the souls in which they inhere exist, and all agree that these are neither visible nor tangible, doesn't this imply that there are things which are incorporeal and which nevertheless exist? Therefore can we not say that anything that has the power to affect another is a thing which exists? Thus isn't it true that the materialists have come a long way from believing that only that exists which can be squeezed in the hand. But from this argument Plato said that we can derive the implication that the definition of being is connected with power, not material.

This leads to his argument from the point of view of the idealists. These would distinguish essence from generation. They would say that we participate in generation through the body and in thought through the soul. But essence remains constant where generation varies. Thus being is an active or a passive energy that arises out of the power that is produced by the elements meeting with one another. But, the idealists would also argue that the power applies to both only in becoming, and not in being. However, if we can say that the soul knows and the being is what is known, then the known is acted upon by knowledge. If, then, all things that are thus acted on then all things are in motion. Thus sameness of condition could never occur, there could be no unchangeable. So there could be no knowledge, and mind could have no existence. Since we must rile against anyone who would annihilate knowledge and reason, then we must say that all is not in motion, we must have knowledge and we must have what is known. Of the movable and the immovable, Plato said, "Give us both." With this statement Plato, often considered the father of idealism, pointed out a feature often ignored in discussions of idealists, that is, that the true idealist must account for those things considered real by the materialists as well as those things the idealists hold as real. Two thousand years later the german philosopher Hegel would put this idealist position in simple terms by stating that what is real does not exist and what exists is not real.

For our purpose we need more than simply a description of Plato's ideas. We need a very specific description of those elements of his thought that made them so important for the development of western civilization and particularly western Christianity. For this we now turn to the Timaeus, to Plato's description of God and cosmology. This statement distills a great deal of Platonic thought in one phrase.

What is that which always is and has no becoming; and what is that which is always becoming and never is? That which is apprehended by intelligence and reason is always in the same state; but that which is conceived by opinion with the help of sensation and without reason, is always in the process of becoming and perishing and never really is.

As you can see, the Eleatic one has been transformed into the world of the unchanging, of the pure forms. The sensual world, Parmenides world of illusion has, in Plato's mature thought, become the world of becoming. Timaeus then posed this question; Was the world created or has it existed from eternity? This is important for Plato's cosmology because it the world has existed from eternity, that is if is eternal, it is part of the unchanging world of the forms. If it created then it implied the existence of a creator. It was to become an important question for Christian thought also because much of early Christian thought absorbed the Platonic view of the universe.

Timaeus' answer was quite simple.

The world is visible, tangible, has a body. Therefore it is necessary that it was created and that it had a cause. But for its pattern, the Creator necessarily looked to the unchangeable. What he meant by the word "Creator" has been debated by scholars for thousands of years. But the idea of a created universe, in opposition to the traditional Greek idea of the eternal universe, requires some entity which accomplished the creation.

Every one will see that He must have looked to the eternal; for the world is the fairest of creations and He is the best of causes. And having been created in this way, the world has been framed in the likeness of that which is apprehended by reason and mind and is unchangeable, and must therefore of necessity, if this is admitted, be a copy of something.

This means that when we use words to describe the world and what is in it, we need only use words that are probable. But, when we are describing the eternal and unchangeable that the world was patterned after, the words we use ought to be lasting and unalterable. For, he said, "As being is to becoming, so is truth to belief."

Why. Timaeus went on, did the creator make this world of generation?

He was good, and the good can never have any jealousy of anything. And being free of jealousy, He desired that all things should be as like himself as they could be.

The Creator began the process of creation by bringing order out of chaos. Since He was creating the best and since no creature devoid of intelligence was as fair He placed within those creatures soul. "The world became a living creature truly endowed with soul and intelligence by the providence of God." It is a whole of which all animals both individually and in tribes are portions. It contains in itself all intelligible beings. Within this world God created one intelligent animal capable of comprehending within itself all other animals.

There can be only one world because the world is a living entity which comprehends all that is. For that which includes all other intelligible creatures cannot have a second. That would require another living being which could comprehend both. Such an individual would necessarily resemble both and both would be parts of this individual. The Creator necessarily made only one world and one created heaven.

This is the final culmination of the centuries of Greek philosophy that led to Plato. The Eleatic one has been turned into the Ideal world after which the world created by God was patterned. This God is the God of Anaximenes and Empedocles rolled into one. He is necessarily all good as was the Zeus of Hesiod and Homer. But he is still an abstraction, impersonal, a derivation of Pythagorean mysticism. Even his description of the world soul as the intelligence of the ideal world is purely abstract.

He took the three elements of the same, the other, and the essence, and mingled them into one form. Compressing by force the reluctant and unsociable nature of the other into the same. When he had mingled them with the essence and out of three made one, he again divided this whole into as many portions of the same, the other, and the essence.

The division of the new whole which is a trinity of the same, the other, and the essence, was done according to the Pythagorean theorem and the diatonic scale. The motion of the other was divided into the orbits of the seven planets. Once the soul was formed he formed within it the corporeal universe.

The soul, interfused everywhere from the center to the circumference of heaven, of which she also is the external envelopment, herself turning in herself, began a divine beginning of never-ceasing and rational life enduring throughout all time.

When reason is dealing with the sensible world there arises opinions and beliefs. The sensible world is not real, it cannot be known. Only when reason is dealing with the rational, the real world, then intelligence and knowledge not only can, but necessarily are perfected. Seeing the greatness of what he created the Father sought to make all eternal. This was not possible. Thus He created an eternal moving image of eternity . This we call time. He constructed days and nights, past and future all of which are created species of time. Note that the moment that God created the past, he made the created world eternal. Plato was without question an active participant in the Athenian culture of his day. His ideas were brilliant expressions of the period and culture in which he lived. They remained a basic source of knowledge for another thousand years despite a few hundred years of neglect under the Romans.

As we will discover, these ideas became mingled with the hotly contested ideas of middle ages Christianity. They formed a rational ground which, when it merged with the Nazarene Jews of the Hellenistic period created a new religion that would sweep the world.