Plato's Theory of Knowledge


Plato's theory of knowledge -to the extent that he had a "theory"- derives from the presumably historical debates between Socrates and the sophists, of which Plato's dialogues give us a vivid picture. The way Plato presents it, the battle between these opponents was the contest between seekers of knowledge (lovers of wisdom), episteme, versus purveyors of opinions, doxa. Thus he begins with the contrast between knowledge and opinion and the question why is one, knowledge, so much preferable to the other, opinion.

Opinion can possibly be true, in which case it serves as a succesful guide to action (and this explains how Athens' heroes were good, they had correct opinions). But even true opinion, because it is only opinion, cannot be defended, and thus "like a runaway slave" flees when attacked. However, knowledge differs from mere opinion in that it can be defended by a logos, a rational explanation of why that opinion is true. Thus emerges the formula that knowledge is true opinion accompanied by a logos, or as it came to be expressed in the Western tradition, as "justified true belief."

This means that the real difference between opinion and knowledge lies in the "justification" (the logos). An opinion can become justified by showing how it can be deduced from other premises, if those premises are true. But no matter how validily we reason, Socrates saw that we cannot justify any opinion unless we start from premises known to be true, rather than just assumed as "hypotheses" in the way the mathematician assumes certain axioms. The series of justifications would seem to be infinite unless some "first" premises can be known directly and not inferred from "higher" premises. How can we attain knowledge of such premises which are not merely possibly true, like a mere hypothesis, but are necessarily true?

Socrates gave us an example of how to search for propositions which could be laid down as necessarily true premises. He thought they could be found by discovering essential definitions through a dialectical process of refuting successive hypotheses until we arrive at one beyond any possible refutation (the "socratic method"). Such definitions are not merely artifical conventions of human language on how to use a word, but are "true" in the correspondence sense of corresponding to what is really the case. Such definitions are thus a kind of direct knowledge and are necessarily true. What is the object of such knowledge?

Plato argued that since such definitions are necessarily true (in order to be distinguished from mere opinions) what they are true of, their objects, cannot possibly change, for if the object were to change, then what is true of them at one time could not be at a later time, thus it would not be necessarily true. Thus the surprising conclusion is reached that the object of knowledge can never change. But everything in the physical world (in space and time) is changeable. All we can know with our senses is in the physical world. Thus objects of sensory experience cannot be objects of knowledge. Thus if there is knowledge, and Plato thinks the example of mathematics establishes that there is, then there must be some "other world" of changeless, eternal objects. Plato's attempt to explicate this "other world" is known as his Theory of Forms.

The theory of Forms begins in the epistemological context of distinguishing knowledge from opinion, but the epistemological distinction between "knowledge" vs. "opinion" immediately implies a metaphysical distinction between what is real versus what merely appears to be so, or in other words "reality" vs. "appearance". Moreover, the ethical question of distinguishing the "truly good" from the "merely appearing good" is never far in the background. Thus the theory of Forms is an epistemological- metaphysical- ethical theory all wrapped into one, or to put it more specifically, the Forms play three roles: epistemological, metaphysical, and ethical.

Epistemologically the Forms appear as the "objects" of knowledge. Knowledge is always "knowledge of..."; or in other words knowledge must have an "object" which it is knowledge of. Knowing what that object is, is essential for an adequate theory of knowledge, an epistemology. If we catch hold of the wrong object, a false illusion, and mistake it to be the real thing, we are in a state of ignorance. Hence the object of knowledge must be what is really so, not what merely appears to be the case. So Plato lays down the crucial claim that the object of knowledge is "real." This is the role that the Form, is called upon to play; by definition, it is the real object of knowledge.

But physical objects we perceive with our senses cannot serve as the objects of knowledge, for what appears, for example, beautiful from one point of view, appears ugly from another; what is beautiful today, may grow old and decay and loose its beauty. Thus the true lover of beauty should not pursue beautiful things, but should seek that which makes the beautiful things beautiful, what all beautiful things "share in" to some degree or another and which makes them beautiful. This is the essence of beauty, it is the "object" the lover of beauty seeks, it is the Platonic "Form" of "Beauty Itself" or as Plato often puts it, "The Beautiful." It is not an idea in a person"s "mind"; it is a real entity existing "own its own" independently from any human (or other) being's idea of it. As the object of knowledge the Form is "seen" with the "mind's eye" (the faculty of nous) in analogy to the way in which opinions take as their objects the beautiful physical objects "seen" with the body's eyes. Thus Forms are the objects of knowledge while physical objects are objects of opinions. The former are "seen" with the mind, the latter with the senses. But it is essential to Plato's view that Forms are not themselves "in the mind".

The metaphysical role of the Forms thus is to distinguish the truly real from the merely appearing. Physical objects present appearances of the Forms, but they are never "perfect" and fall short of the "ideal" set by the Form. A drawing of a circle, no matter how carefully constructed, is never the geometer's perfect circle, the object of geometrical knowledge. What is physical and can be grasped with the senses is always changing, coming into being and perishing. It thus lies "between" what truly is, the Form, and "that which is not," the object of complete ignorance. So just as "opinions" can be said to lie "between" knowledge and ignorance, the objects of opinion lie between Being and Non-being, they are said to be in a state of "Becoming" for they are always becoming something else, they are never purely and simply "what is."

Thus the theory of Forms gives Plato a "two-level" metaphysics or theory of the nature of reality. One level is called the "Realm of Being" containing the Forms. These are the true realities, the objects of knowledge. They neither change nor come into being or perish; they are eternal. Each one is absolutely unique and different from the others; there is only one Form of the Just, one of the Beautiful. etc. If you and I differ about what is "just" we cannot both have knowledge, one or the other or possibly both of us have mistaken opinions. The unity of each Form guarantees that those who have knowledge will always agree, for they "see" with their minds the same one reality. Furthermore, the fact that knowledge takes as its objects the Forms and that the Forms are changeless and eternal guarantees that knowledge is "necessarily true" in the sense that it if we have genuine knowledge, what we know to be true today cannot be false tomorrow; knowledge is eternal. By contrast, opinions which take as their objects the physical objects we perceive with our senses can be true at one time and false at another, for such objects change. Opinions are therefore capable of being true at one time and false at another; they are said to be "fallible" whereas knowledge is "certain." Thus Western philosophy comes to regard the search for knowledge as, in Dewey's phrase, "the quest for certainty."

Physical objects, seen by the bodily senses, form the second level of Plato theory of reality; they exist in the "Realm of Becoming." This is the physical world, the world of space and time in which one's body dwells. Such objects come into being and perish, they are constantly "in flux", changing. What is true of a physical object today may be false tomorrow; thus our state of mind regarding physical objects must always be restricted to fallible opinions.

However, physical objects are not totally un-real, for they really are, at least for the moment, this or that to some extent or another. They have this degree of reality because physical objects bear a relationship to the Forms; Plato says they "share in" or "participate in" or "reflect" or "copy" or "imitate" the Forms. (The nature of this relationship is always somewhat elusive, and in his elder years Plato himself directed stinging criticisms against the theory on this grounds.) The basic idea is that something is what it is to the extent that it shares in the Form of that thing; to the extent that it fails to do so, it fails to be that thing. A man is "just" to the extent that his life "participates in" the Form of Justice Itself, and "unjust" to the extent that it fails to do so. Thus the metaphysical role of the Forms is that they make things what they are.

The Ethical role of the Forms lies in the fact that the Forms found in the Realm of Being are the perfect ideals of that of which they are the Forms. "The Just Itself" can in no way be unjust, it is purely, fully, really just; it is "perfect" justice. Thus it serves as a "yardstick" or "natural standard" against which to measure the degree of justice in this or that person's life. This standard has a objective reality quite apart from human opinions about justice and injustice; it determines what really is just, not merely what appears in the false opinions of people to be just. So all of the virtues which Socrates was questioning about now emerge as Forms in Plato's theory as Forms.

The definitions Socrates sought required, in effect, a mental "vision" of the Forms. These are the ultimate premises from which any justification must be inferred, thus the mind's mental vision or "recognizing" (noesis) of the Forms provides the basis of all knowledge.