Plato on Knowledge and Perception
Most of us modern people would take empirical knowledge for granted or derive from perception. Plato and certain schools of philosophers, however, argued that there is nothing worthy of feeling called "knowledge," and that true knowledge must be related to concepts. This view can be traced back to Parmenides, who was discussed by Plato in the Teatides through a critique of the idea that knowledge and perception are one thing.
The dialogue proposes the first definition of knowledge through the mouth of Thated: "For me, the person who knows something is aware of what he knows, and as far as I can see at the moment, knowledge is nothing but perception. His interlocutor Socrates equated this definition with protagoras' statement that "man is the measure of all things," adding: "Then perception is always something that exists, and it is infallible as knowledge." Then he made a large argument about the characteristics of perception, and after the discussion, he proved that such a thing as perception could never be knowledge! (Consistent sophistry)
Socrates added Heraclitus's theory that everything is in flux to Protagoras' doctrine. Plato believed that this was true to the object of sensation, but not to the object of real knowledge. So putting together Heraclitus's doctrine and defining knowledge as perception leads to the conclusion that knowledge is about things that change, not about things that exist. (They deny that what exists is also something that changes.)
Perception is thought to be the result of an interaction between the object and the sensory organs, and according to Heraclitus, both are always changing, and in the process of their change they are changing the object of perception. Socrates makes an interesting idea that when one view cannot be more true than the other, it can be better—in the sense that it leads to better consequences. This statement is reminiscent of pragmatism, and it is natural to conclude that a wise man is a better measure of all things than a fool.
With regard to the theory of change in all things, we should realize that whatever else is in eternal flux, the meaning of words must be determined at least for a certain period of time, otherwise no proposition is certain, and no proposition is true and not false. If discussion and knowledge are to be possible, there must be something more or less consistent. This should be acknowledged.
Plato's final argument against the equality of knowledge to perception began. There is no specialized organ to perceive "existence and non-existence, similarity and dissimilarity, identity and dissimilarity, and mathematically homogeneous numbers versus general numbers," he said. Only the mind can recognize existence, and if we do not know the existence of things, we cannot know the truth. So knowledge lies in contemplation and not in impression. Perception is not equal to knowledge, for "since perception does not comprehend what exists, the understanding of truth has nothing to do with it."
Plato's argument against the equality of knowledge with perception, which has both acceptable parts and some that must be rejected, involves three related propositions, namely:
1, knowledge is perception;
2, man is the scale of all things;
3. Everything is in a rheological state.
With regard to the first proposition, it is clear that much knowledge does indeed come from human perception, and it is through the perception of various sensory organs that human beings form, and summarize and unify the meaning of this perception, forming universally recognized knowledge, that is, empirical knowledge. However, Plato's view that arithmetic and pure mathematics in general do not come from perception is acceptable. To know whether a mathematical proposition is correct, we don't have to study the world, we just need to study the meaning of symbols. This is what formal logic requires, which does not require the involvement of sensory organs.
With regard to the second proposition, "Man is the measure of all things," the most fundamental thing is at which level we should discuss this. As objects of the same perception, because their background environment may be different, it is easy to lead to erroneous inferences. And where did the inference come from? We must admit that some inferences are private and personal, and that they are full of subjective assertions. Plato seems to be right again on this question. But there is some kind of impersonal correct criterion for inferences as opposed to perception. Moreover, empiricists would say that perception is the criterion for testing the correctness of inferences made by empirical material.
Finally, let's look at Proposition Three. The doctrine of universal change was exaggerated and distorted by Plato. Plato came to his conclusion because he applied the logical dualities of perception and non-perception, knowing and not knowing, to the process of continuous change. These opposites are not really suitable for describing processes. Logical oppositions are created for our convenience, but to study continuous change requires a means of measurement, and Plato ignores the possibility of finding such a means. (Calculus is an effective means for human beings to study the continuity of change.)
Finally, we must acknowledge that words have a definite meaning in some sense, otherwise discussion is impossible. However, this is just as prone to the mistake of absolutization. The meaning of words is indeed constantly changing. It is necessary for the change in the meaning of words to lag behind the change of things described in words, but there is no need to be completely unchanged. (Readers can experience the change in the meaning of many words, such as "sir", "miss", etc.)