Essentials of Philosophy and Christian Thought - Lesson 4

Plato: Theory of Knowledge

Plato's doctrine of the immortality of the soul, his understanding of knowledge (argued against by Augustine and Plotinus), and a discussion of rationalism vs. empiricism

Ronald Nash
Essentials of Philosophy and Christian Thought
Lesson 4
Watching Now
Plato: Theory of Knowledge


Part 2

II. Plato’s Theory of Knowledge

A. Plato on Immortality of the Soul

B. Plato’s Argument

C. Plato’s Argument Refuted

1. Augustine

2. Plotinus

D. Rationalism vs. Empiricism

  • Dr. Nash covers the objectives to the lectures, reading material, and discusses the five major beliefs that make up a worldview

  • A discussion of naturalism, what it teaches, two major exponents of naturalism (Lamont, Russell), and why it is wrong

  • Theories opposed by Plato ("Hermman"), his significance, his three forms of dualism, and Plato's basic teaching on "forms"

  • Plato's doctrine of the immortality of the soul, his understanding of knowledge (argued against by Augustine and Plotinus), and a discussion of rationalism vs. empiricism

  • The contributions of Aristotle (the law of non-contradiction; the difference between essential and non-essential properties), Plotinus, and Aquinas

  • Open theism is the belief that God does not know the future; otherwise, we would not be free in our decisions. Nash discusses the teachings of God's omniscience and human free will, and the logical implications of this teaching.

A seminary-level version of this class is available in our Institute Program.

Dr. Ronald Nash

Essentials of Philosophy and Christian Thought


Plato: Theory of Knowledge

Lesson Transcript


Alright, now, remember that within the context of the book of Life’s Ultimate Questions, and within the context of the longer course, I go on and discuss in much greater detail the five major parts of Plato’s worldview. I talk about his view of God. I have just told you about Plato’s metaphysics, his belief that the world exists in two levels—the lower world and the higher world, the world of forms and the world of particular things.

I’m going to talk about one more thing with Plato and then we’re just going to have to leave you to pursue the rest of what you might want to know about Plato either from my books or from a longer tape. But I do want to talk about Plato’s theory of knowledge because this is very important. It has important ramifications. And so I’m going to talk about what I think may be one of the most important philosophical passages in the entire history of philosophy. And most philosophers read/write past this material—they do not pay any attention to it.

It occurs in a dialogue that Plato wrote called the Phaedo. Now let me tell you something about Plato’s dialogues. They are divided into three groups. They’re called the Early Dialogues, the Later Dialogues, and the Middle Dialogues. And the Phaedo is one of Plato’s middle writings. Now here are some of the differences among these writings. In the early writings of Plato, the central figure is usually Socrates, and there is often little of great philosophical significance in the early dialogues. In fact, in the dialogue called the Apology there may be no real philosophy at all—it’s just the story of Socrates’ trial, the charges that were brought against Socrates. In another early dialogue, you have Socrates waiting in jail to be executed.

But in the Phaedo, you have what is supposed to be the last meeting between Socrates and his disciples before he is executed by drinking hemlock. Because this is a middle dialogue, the Phaedo, scholars believe that by this time in his life Plato was taking liberties with the historical Socrates and was actually using Socrates as a spokesman for his own ideas. In the later dialogues, such as the Timaeus, for example, and I just mention that in passing, there are times when Socrates doesn’t appear at all—he does appear in Timaeus, but sometimes [Plato] uses an Athenian stranger or some other character to expound his ideas.

The Phaedo is probably written early in Socrates’ middle period. One reason why we know that some of the material is not historically accurate is because Plato puts into the mouth of Socrates his very important theory of the forms. The dialogue assumes this form very quickly. Socrates is asked to prove the immortality of the soul. In response to that question, Plato puts into the mouth of Socrates a number of arguments that he apparently thinks prove the immortality of the soul when in fact the arguments are quite, quite bad. Even though this argument I’m going to look at with you fails as a proof of the immortality of the soul, it nonetheless directs our attention, I think, in a magnificent way to help us understand the basic principles of what we call Plato’s Rationalism.

Now, Plato’s disciples have asked him to provide a proof of the immortality of the soul, and he proceeds by inviting them—again, using Socrates as a spokesman—he begins by inviting them to think about the concept of equality. Now, what we mean by equality here is the fact that two line segments might have the same length, or two triangles might have the same size—that kind of equality. And Socrates asks his friends: What must you know in order for you to know that two things are equal—like two line segments, two sticks, two triangles—what must you know before you know that two things are equal? Well, first of all, you have to have information about the size of this line segment, you have to have information about the size of these triangles. And how do you acquire that information? Through your sense organs. You see, you touch, you evaluate. But you must know something else before you can know that two things are equal. You have to know what the concept of equality is. You cannot know that two things are equal unless you first know what equality is.

Then Socrates says you cannot know the concept of equality through your senses because everything that you perceive through your senses is changeable, is non-eternal, is non immutable. But the concept of equality is changeless. It cannot change, it never changes. So, what is the only way in which you can know what equality is? And his answer is through your mind, through your reason.

Now, Plato had another peculiar characteristic. His writings are full of what we call myths. Now the word ‘myth’ has a number of different meanings. What it means in Plato’s situation is this: It is a likely story. It looks very much as though every time Plato bumped up against a question which he really couldn’t answer, he told a story. And it is debatable as to whether, if ever, he meant these stories to be taken literally, truthfully. It’s very much as though Plato said, “You’ve just asked me a question, in this case, the question is: How do we know the concept of equality? And I’m going to tell you a story, and I don’t know whether the story is true or not, okay?”

Now, it turns out that Plato actually changed his mind on a number of occasions. And that what was his story at the time he wrote the Phaedo as to how human beings come to know that two things are equal, how that human beings come to know that this is a beautiful object, etc.—Plato changed his mind. Here was his story at the time he wrote the Phaedo. He said that he believed in reincarnation. He said that he believed in reincarnation. And here’s how the theory of reincarnation came to  his aid. He said that when human beings die their body, of course, goes into the grave, but their soul leaves this body and goes to the world of the forms, remember, that world of perfect, unchangeable essences that exists somewhere, somehow—he never really makes that plain. And while the soul is in the world of the forms it there perceives these unchanging forms like truth, and beauty, and goodness, and justice, and equality, so that the soul really knows what the true nature of these concepts is. But then, given his theory of reincarnation, he says human beings return to this life either as other human beings or sometimes as other animals.

Let’s assume the case of a human being who’s going to go through, oh, let’s say, reincarnation number 100, alright. We can even give this human being a name—we can call her Shirley, as in Shirley MacLaine, who tells us that she too believes in reincarnation. So, let us say that Shirley died at the end of life number 99. Shirley’s soul, to follow Plato here, goes to the world of the forms. Shirley’s soul apprehends the world of the forms, the concept of equality, and then Shirley reenters the human life in another incarnation. When Shirley is—I don’t want to use the term ‘born again’, because that is very misleading and that, of course, would be to misuse a very important Christian concept—but let’s say that Shirley is born into life number 100, she forgets, as a condition of being born into reincarnation, or life number 100, she forgets everything that she has seen about the forms. But even though she forgets them, that knowledge of the concept of equality is still present in her mind subconsciously. And as young Shirley grows us and sees things through her young life as a child, she is able to recognize that these things are equal because the knowledge of equality has been present in her mind unconsciously since birth, you see.

So Plato comes up with an argument to explain how human beings and their souls must exist between death and rebirth. And the reason why we can believe that is because as we develop and mature in a particular life we keep demonstrating our recognition, our memory of certain things that we must have been born with, innate ideas.

But here is Plato’s argument. It has two premises and two conclusions. The first premise is this: All human knowing presupposes a prior knowledge of some form or rule or standard. In other words, the fact that human beings can recognize that two things are equal even though we’ve never been taught it, even though we’ve never seen true equality with our physical senses, proves that we must have known this before this current life began. Ok? All knowing presupposes a prior knowledge of some rule or form or standard, and the reason we can recognize that two stones are equal is because we have known the concept of equality from the beginning of this life.

Secondly, Plato teaches, human knowledge of this form or standard or rule, such as the nature of equality, human knowledge of that form cannot be acquired through the senses, it cannot be acquired through teaching, it cannot be acquired through this life. In other words, our knowledge of the concept of equality must be innate; it’s born within us. It must therefore be something we had before this life began.

So that leads Plato to his first conclusion, that human knowledge of the forms is acquired in an earlier existence. We know the concept of equality in this life because we’ve known it in a previous existence. And finally, that brings Plato—see, we’ve got two premises, and we’ve got two conclusions—that leads us to the last of Plato’s conclusions: Therefore, the human soul is immortal. It has always existed.

Now that’s the very interesting argument that Plato offers in the Phaedo. It’s a bad argument; don’t believe it. Now, I suppose there are people in California who think that way today, but don’t you think that way. Here’s why that’s a bad argument to prove the immortality of the soul.

Let’s start at the bottom and let’s move upward. First of all, does the fact that the human soul lived in a prior life prove that the human soul is immortal? Of course not. When we talk about immortality, what we want to know is not whether I might have existed in a previous life. What I want to know when we raise the question of what immortality is whether I’m going to continue to live the next time I die, see. It does not follow that just because you lived in a previous life your soul is presently immortal—that’s a bad argument.

Let’s go back one further step. Does Plato claim that the idea of equality or any of these other ideas is inborn, is innate, does that prove we existed in a prior life? Of course not. Now here’s the proof for that, here’s the argument for that. And it introduces us to the man whom I think is the most important […] of the history of philosophy, at least from my book, and at least from my corpse. If you want to think somebody else is more important, you make your own tape and you write your own book. But it was St. Augustine. Now who was St. Augustine? Well I’m going to tell you more about him shortly. But he was a man who was born in 354 AD to a Christian mother, a wonderful Christian mother names Monica. But when he went away to the university, he really rebelled against his mother’s religion. And, in fact, he resisted Christianity, he fought against Christianity from about the age of seventeen to about the age of—well, for a good thirteen, fourteen, fifteen years—thirty-three. But when St. Augustine became a Christian, and I’ll tell you about his conversion in a little while, he was saved from all kinds of bad errors in his thinking by his introduction to a Platonist named Plotinus. Plotinus was not a Christian thinker—I’m going to say a little bit about him, a very little bit about him in a short amount of time. Augustine had wandered away from the Christian faith of his mother and he had begun to pursue several bad worldviews, but he ran across the thinking of Plotinus and it helped deliver him from some bad errors. And one of the important things that Augustine learned from Plotinus was this: That all these forms that Plato had talked about, these eternal essences, Plato never really knew what these forms were, he never really knew where they existed, he just said there’s a world of forms and sometimes it sounds as if they just float around the universe at some point. What later Platonists did was to begin to think of the forms of Plato as ideas in the mind of an eternal God. And Augustine picked up on that and it changed Augustine’s whole understanding of the world. Of course, the fact that Augustine also met Jesus and became a Christian, that also played a part as well.

Now, let’s go back to Plato. Plato had said all human knowledge arises from a prior knowledge of some form or rule or standard, like equality, ok. And then Plato said we cannot get this knowledge of the concept of equality or any other of these universal concepts from sense experience, we cannot learn it in this life, we cannot get it through teaching. But that’s where Plato made his big mistake. He said, therefore, we must understand that these forms are known from earlier experience, from an earlier life. Augustine said not on your life, here’s how we acquire our knowledge of these eternal ideas: God, who created man—this is the gospel--God, who created man, gave us an innate idea, an innate understanding of these ideas, which have always been eternal ideas in the mind of God. So how do I know the concept of truth? How do I know the concept of beauty? How do I know the concept of justice? How do I know the concept of equality? According to the great St. Augustine, he said: I know these things innately from birth because God gave me these ideas as a part of the image of God. So we can forget all this nonsense about the preexistence of the soul. None of this has anything at all to do, essentially, with immortality. Plato was all wet when he talked about that material, but, nonetheless, Plato helps us recognize through the guidance provided by St. Augustine in to how the mind of God and the creation of the human mind by God explains how we come to know these things from birth, or innately, alright, not by sense experience but by reason, by the mind.

Now I’m going to get back to Augustine in a short while, but, and here I’ve got to stop. Let me just take a few minutes here to explain the basic difference between rationalism and empiricism. Let me explain here the basic difference between rationalism and empiricism. And I want to do that by using a little device that Aristotle invented, or discovered, called the square of opposition. Now hang in here with me. If you’ve got the book and you can access that book, this would make it a lot easier, but, you know, we can get along without the book too.

Aristotle made the distinction between four propositions. Here they are. It might help you to write these down, and write them down in the form of a square, okay? At the left hand top corner of the square, write this sentence: All S is P. That’s real tough. All S is P. On the upper right, write this: No S is P. Lower left, write: Some S is P. In the lower right, r-i-g-h-t, write, w-r-i-t-e: Some S is not P. Alright. So, in the form of a square you’ve got: All S is P, No S is P, Some S is P, and Some S is not P. Okay. Let’s give these four options names as they did during the Middle Ages. Let’s name them after the four vowels. So the proposition ‘All S is P’ is the A proposition. ‘No S is P’ is the E proposition. ‘Some S is P’ is the I proposition. And ‘Some S is not P’ is the O proposition.

Now, let’s get more specific here. Let the A proposition now become ‘All human knowledge arises from sense experience’—‘All human knowledge arises from sense experience’. Believe me when I tell you that this is really the definition of empiricism. I don’t care whether you look at Aristotle; I don’t care whether you look at Aquinas; whether you look at the other famous empiricists in the history of philosophy, this is the belief of empiricism, that the basic building blocks of all human knowledge is sense experience. Without sense experience, we cannot know anything. Okay? That would be Aristotle’s position. That would be, in my understanding, Aquinas’ position—All human knowledge arises from sense experience.

The E proposition goes like this: ‘No human knowledge arises from sense experience’. That was Plato’s view. Please notice it is not my view. Let us call Plato a kind of radical rationalist. Plato [had] no use for sense experience at all—he was an enemy of any kind of sense experience.

Now forget the I proposition—that’s irrelevant to our discussion here. But the O proposition is not. How does the O proposition go? ‘Some human knowledge does not arise from sense experience’. Now, that is my definition of rationalism. See, many people, I think, most people here have the mistaken idea that if you are a rationalist, and there’s no doubt that Plato was, if you’re a rationalist you must discredit all sense experience. You must postulate that no human knowledge comes through sense experience, which leaves you discrediting the human senses. Now what Augustine, and Ron Nash, and a whole lot of other smart people do—and I’m being a little cynical here—what Augustine, and Ron Nash, and a whole lot of other great people do, is they recognize that all that’s necessary for rationalism to be true is that just one item of human knowledge arise through some means other than sense experience. I do not deny the importance of sense experience; what I deny is that sense experience provides the foundation for all human knowledge. Now what kinds of human knowledge do not depend upon sense experience? Your knowledge of the equal itself, your knowledge of goodness itself, you knowledge of truth itself, your knowledge of justice—these fundamental, eternal ideas that Plato talked about but didn’t know what to do with, and that Augustine talked about and explained them as eternal ideas that exist forever in the mind of God, your knowledge of these does not depend upon sense experience. And if you just knew one thing like the nature of truth, or the nature of beauty, or the concept of equality, or the concept of oneness, if you knew just one thing without sense experience, that would make you a rationalist.

Now one other comment here. Empiricism has one major disadvantage, and that major disadvantage is that if you’re an empiricist you have to be able to prove that every piece of human knowledge can be traced back to sense experience. But, you see, if you’re a rationalist, you’ve got a lots—you’ve got a much simpler job. All you have to do to prove rationalism is to come up with one eternal idea that human beings can know without sense experience. Do you follow me? Now, the history of philosophy is full of empiricists. I don’t think you can maintain that position consistently. I am proud to be called a rationalist.

In fact, let me tell you a true story. After I gave the first of many lectures in the Soviet Union, later, Russia, back in 1991 and 1992, a professor came up after my lecture in Moscow and told me that she thought I had done a good job. Well, you know, in my business, you always wait for the ‘but’. I had done a good job at explaining some philosophical things, but she said: You are too much of a rationalist. Now let me tell you something. When people call me a rationalist, I thank them. I appreciate it. Because do you know what the opposite of rationalist is? Irrationalist. Now, this lady misunderstood what I was trying to do, actually, I didn’t exactly understand the basis for her criticism, although I did later that day when she and I met with a translator. And I discovered, to my amazement, that this Soviet professor of philosophy was actually teaching the theories of Plotinus. This guy that I’ve continued to mention by name but about whom you know probably nothing right now. And once I understood what she was getting at I explained to her that she was citing the ideas of man named Plotinus who had died in Rome in 270 AD and she didn’t know that. My position on epistemology is the moderate rationalism of St. Augustine which amounts to the claim that human beings know some things that they do not learn through their senses.

Okay. Well, there’s a whole lot more about Augustine and Plato but we’ve got to move on. This is a summary. There’s lots of great stuff in the full tape. I talk about Plato’s view of creation and Augustine’s view of creation and how the Christian view is superior to that of Plato’s. But we must move on.