Chapter 21 Chapter 18 Knowledge and Perception in Plato's Philosophy

Most modern people take it for granted that empirical knowledge must depend on, or be derived from, perception.Yet among Plato, and certain other schools of philosophers, there is a quite different doctrine, to the effect that nothing worthy of the name "knowledge" comes from the senses, and that the only true knowledge must be about concepts.On this view, "2 + 2 = 4" is true knowledge; but a statement like "Snow is white" is so full of vagueness and inaccuracies that it has no place in the philosopher's system of truth. This view may be traced back to Parmenides, but philosophy owes its definite form to Plato.In this chapter I am only going to deal with Plato's criticism of the view that knowledge and perception are the same, which takes up the first half of his Theaetetus.

The dialogue was supposed to seek a definition of "knowledge," but it did not lead to anything but a negative conclusion; several definitions were proposed and then rejected, and no one was ever brought up that would suggest Definition of Satisfaction. The first definition proposed, and the only one I shall consider, is that of Theaetetus as follows: "It seems to me that a man who knows something perceives the thing he knows, and all I can see so far is that knowledge is nothing but perception." Socrates equates this doctrine with Protagoras's that "man is the measure of all things," that whatever is "to me is what I see, is to you." The way you see it."Socrates added: "Therefore perception is always something real, and it is infallible as knowledge".

A large part of the argument that follows is devoted to the character of perception; and having dealt with this, it soon proves that such a thing as perception forms can never be knowledge. Socrates adds to that of Protagoras the teaching of Heraclitus; Heraclitus says that all things are perpetually changing, that is to say, everything "that which we please call real, substance Everything is in a process of change.”Plato believed this to be true of the objects of sense, but not of true knowledge.Throughout the dialogue, however, his positive doctrine remains in the background. Adding Heraclitus' doctrine (even if it applies only to objects of the senses) and the definition of knowledge as perception, it follows that knowledge belongs to things that change, not to things that are. of.

At this point, there are some fundamental difficulties.He told us that since 6 is greater than 4 but less than 12, 6 is both large and small at the same time, which is a contradiction.Another example is that Socrates is taller than Theaetetus, and Theaetetus is a young man who has not yet grown up; but after a few years, Socrates will be shorter than Theaetetus.So Socrates is tall and short.This idea of ​​a relational proposition seems to have stumped Plato, as it has stumped most of the great philosophers up to and including Hegel.These difficulties, however, are not very relevant to this argument and may be ignored.

Returning to perception, perception is considered to be due to the interaction between objects and sense organs.According to Heraclitus, the latter two are always changing, and as they change, they also change perception.Socrates said that wine was sweet to him when he was healthy, but sour when he was sick.Here it is the change of the perceiver that causes the change of perception. Some objections to Protagoras' theory were also raised, some of which were later withdrawn.Some questioned that Protagoras should equally admit that pigs and baboons are also the measure of all things, because they are also perceivers.Questions have also been raised about the validity of perception in dreams and in madness.It was mentioned that if Protagoras was right, no one knew better than others: not only was Protagoras as wise as the gods, but more seriously he was no better than a A fool is wiser.Moreover, if every man's judgment was as right as that of the others, he who judged Protagoras to be wrong would just as well be considered as right as Protagoras.

Socrates comes out and puts himself temporarily in Protagoras' place, and finds an answer to these objections.As far as dreaming is concerned, perceptions are still true as perceptions.As for the pig and baboons argument, it was dismissed as a vulgar joke.As for the other argument, that if every man is the measure of all things, then every man is as wise as any other; and Socrates, on behalf of Protagoras, offers a very interesting answer, namely, One judgment is not necessarily more true than another, but it can be better than another in the sense that it has better consequences.This hints at pragmatism.However, although Socrates invented this answer, it did not satisfy him.For example, he insisted that when a doctor predicted the course of my illness, he actually knew more about my future than I did.Or when men differ as to what it is wise for the state to enact, the dispute shows that some have more knowledge of the future than others.Thus we cannot escape the conclusion that a wise man is a better measure of all things than a fool.

All this is against the doctrine that man is the measure of all things, and only indirectly against the doctrine that "knowledge" is "perception," since the latter doctrine leads to the former.However, there is also a direct argument that we must admit memory as well as perception.Having agreed to this, the originally proposed definition is then revised to this extent. Next, we come to the criticism of Heraclitus's doctrine.This, it is said, was at first carried to extremes, according to the practice of his disciples among the handsome youths of Ephesus.Everything can change in two ways, one by motion and the other by change of nature; and the theory of rheology holds that all things are always changing in both ways.And not only is everything ever undergoing some kind of qualitative change, but everything is ever changing in its entirety,--so the wise men of Ephesus are said to have thought.This had very embarrassing consequences.We cannot say "it is white," because if it is white when we begin to say it, it will cease to be white before we have finished saying it.It is not true to say that we are seeing an object, because seeing is constantly becoming invisible.If everything changes in all ways, seeing has no right to be called seeing and not seeing, or perception to be called perceiving instead of unaware.And when we say "perception is knowledge," we can equally say "perception is non-knowledge."

The above argument amounts to saying that, whatever else there may be in the constant flux, the meaning of words must, at least for a certain time, be fixed; No assertion is more true than false.If discussion and knowledge are to be possible, there must be something more or less constant.I think this should be admitted.But much of rheology is consistent with this admission. Speaking of this, Plato refused to discuss Parmenides on the grounds that Parmenides was too great and too noble.He is a "respectable and awesome character". "He has a very noble depth".He is "a man I respect most".These words of Plato show his love for a static universe, and his dislike of the Heraclitean flux which he has admitted for the sake of his argument.But having shown this homage, he took pains to avoid substituting Heraclitus for the theory of Parmenides.

We now come to Plato's final argument against knowledge being equal to perception.He begins by pointing out that we perceive through the eyes and ears, not with the eyes and ears; then he goes on to point out that some of our knowledge is not connected with any sense organs.For example, we can know that sound is different from color, although no sense organ can perceive both.There is no particular organ for the perception of "being and non-being in general, likeness and dissimilarity, identity and difference, oneness and manyness."The same applies to honor and dishonor, good and bad. "The mind thinks some things through its own faculties, but others through the faculties of the body."We perceive hardness and softness through the sense of touch, but it is the mind that judges their existence and their opposition.Only the mind can reach Being; but if we cannot reach Being, we cannot reach Truth.Therefore we cannot know things through the senses alone, because through the senses alone we cannot know whether things exist or not.Knowledge therefore consists in thinking and not in impressions, and perception is not knowledge; for perception "being totally incapable of knowing existence, it has no share in the knowledge of truth." It is not easy to know what is acceptable and what must be rejected. There are three interrelated themes discussed by Plato, namely: (1) Knowledge is perception; (2) Man is the measure of all things; (3) ) Everything is in a state of flux.

(1) The first topic (to which Plato's argument mainly deals only) has hardly been discussed in itself, except in the last passage of which we have just been concerned.What is being argued here is that comparison, knowledge of being, and understanding of numbers—these are the most essential things for knowledge, but these cannot be included in perception, because they are not obtained through any sense. produced by organs.Regarding these, what we are going to talk about below is different.Let's start with similarity and dissimilarity.Suppose there are two patches of colour, both of which I am seeing, whether they are actually similar or not, but which I, as far as I am, should accept, and certainly not as a "perception" Rather, it is accepted as a "perceptual judgment".I should say that perception is not knowledge, but merely something that happens; it belongs equally to the physical world as to the mental world.It is natural for us, like Plato, to imagine perception as a relation between the perceiver and the object: we say "I see a table".But the "I" and "table" here are logical constructs.The core of the raw matter here is nothing more than the color of certain fragments.These colors are combined with tactile images, they can evoke words, and they can be the source of memories.The perception filled with tactile images becomes an "object", and it is considered physical by us; while the perception filled with words and memories becomes a "perception", which is Be part of the "subject" and be considered psychological by us.Perception is only an event, neither true nor false; but perception, filled with words, is a judgment, which may be true or false.I call this kind of judgment "perceptual judgment". The meaning of the proposition "knowledge is perception" must be interpreted as "knowledge is perception judgment".It is only in this form that it can be grammatically correct.

Returning to the question of similarity and dissimilarity; when I perceive two colors at the same time, it is very likely that their similarity and dissimilarity are part of the perception and material, and can be confirmed by perceptual judgment.Plato's argument that we do not have sense organs to perceive similarity and dissimilarity ignores the quality of the brain and assumes that all sense organs must be on the surface of the body. The arguments for considering similarity and dissimilarity to be included in possible perceptions and data are as follows.Suppose we see two pieces of color A and B, and suppose we judge that A and B are similar.Let us go a step further and assume, like Plato, that such judgments are true in general, and in particular in the case under consideration.There is then a relation of resemblance between A and B, and not merely a judgment on our part to judge resemblance or non-resemblance.For if there were only our judgment, it would be an arbitrary judgment, and there could be no truth or falsehood.Since it is obviously possible to be true or false, the similarity exists between A and B, and cannot be merely a "psychological" thing. The judgment "A is similar to B" is true (if it is true) because of a "fact," just as the judgment "A is red" or "A is round" is true. of.The mind's perception of similarity or dissimilarity is no more related than the mind's perception of color. I will now come to being. Being. This is what Plato puts so much emphasis on.He said that we have a thought about sound and color that can contain both, and that is that they exist.Being belongs to all things, and is one of those things that the mind itself can know; truth cannot be reached without reaching Being. Here we are refuting Plato's argument, which is quite different from the refutation of similar and dissimilar arguments above.The argument here is that everything Plato says about being is bad grammar, or rather bad grammar.This point is important not only in relation to Plato, but also for other topics such as the ontological proof of the existence of God. Suppose you say to a child "lions exist, but unicorns don't exist", you can take him to the zoo and say "look, that's a lion"; thus proving your thesis about lions .But unless you're a philosopher, you don't add: "Now you can see that there is."But if you're a philosopher and you really add that, you're talking nonsense.To say "lions exist" is to say "there are lions," that is, "'x is a lion' is true for a proper x." But we cannot speak of a proper x and say that it "exists"; We can only apply this verb to a complete or incomplete description. "Lion" is an incomplete description because it can be applied to many objects: "the largest lion in this zoo" is a complete description because it can only be applied to one object. Now suppose I'm looking at a field of bright red.I can say "This is my present perception," and I can also say "My present perception exists"; but I must not say: "This exists," because the word "exist" is used only in connection with a name. Only when it is a description of opposites is it meaningful.This treats being as one of the things the mind perceives in the object. Now I will talk about the understanding of numbers.There are two very different things to be considered here: on the one hand, propositions of arithmetic, and on the other hand, empirical propositions of counting. "2+2=4" belongs to the former category; "I have ten fingers" belongs to the latter category. I should agree with Plato that arithmetic and pure mathematics in general do not arise from perception.Pure mathematics contains tautologies akin to "man is man", but often just more complicated.To know whether a mathematical proposition is true, we do not need to study the world, but only the meaning of symbols; and symbols, when we omit the definition (the purpose is only for simplification), are nothing more than "or" and "not " and words like "all" and "some" and so on, which, unlike "Socrates," do not denote anything in the real world.A mathematical equation affirms that two sets of symbols have the same meaning; and this meaning must be one that can be understood without our knowledge of anything perceptible, so long as we confine ourselves to pure mathematics.Mathematical truth, therefore, is, as Plato says, independent of perception; it is a very peculiar kind of truth, and concerns only signs. Counting propositions, such as "I have ten fingers," are of a different kind entirely, and are obviously (at least in part) dependent on perception. The concept of "fingers" is clearly abstracted from perception; but what about the concept of "ten"?Here we seem to have reached the true universal, or Plato's idea.We cannot say that "ten" is abstracted from perception, because any perception of something which can be regarded as ten can also be regarded as other number.If I use the name "fingers" to refer to all the fingers of a whole hand; then I can say "I have two fingers" and this describes the same finger that I described before with the number ten. Perceived facts.Thus in the statement 'I have ten fingers' than in a statement 'This is red' percepts play less and concepts more.The problem, however, is only a matter of degree.Concerning the propositions in which the word "ten" appears, our complete answer is: when we analyze these propositions correctly, we can find that they contain nothing corresponding to the word "ten".It is more complicated to explain this with the example of a number as large as ten; so let us say "I have two hands" instead.This means: "There is an a and there is a b, and a and b are not the same. 'x is a hand of mine' is true if, and only if, x is a or x is b, whatever x might be". The word "two" does not appear here.It is true that the words a and b occur, but we do not need to know. They are two, just as we do not need to know whether they are black or white, or may have any other color . Therefore, in a strict sense, numbers are forms.The facts which suffice to justify the various propositions which assert that there are various combinations of two components, have in common not a component but only a form.In this they differ from propositions about the Statue of Liberty, or the moon, or George Washington.Those propositions all refer to a particular part of space-time, which is common to all the statements that can be made about the Statue of Liberty.But between such propositions as "there are two so-and-so" there is nothing in common except a common form. The relation of the sign "two" to the meaning of a proposition in which it appears is much more complicated than the relation of the sign "red" to the meaning of a proposition in which the red letter appears.In a sense we may say that the sign "two" does not mean anything; for when it occurs in a true sentence, there is no equivalent constituent in the meaning of the sentence.We can also say, if we like, that numbers are eternal, unchanging, etc., but we must add that they are all logical figments.There is another point.Regarding sound and color, Plato said that "the two together are two, and each of them is one".We have considered two; now we shall consider one.There is also a fallacy in this, very similar to the fallacy about being. The predicate "one" does not apply to things, but only to a single class.We can say "the earth has a satellite"; but it would be a grammatical error to say "the moon is one".For what could such an assertion mean?You can also say "the moon is many" because the moon has many parts. To say "the earth has a satellite" is to give to the concept "satellite of the earth" a property of the following: "There is such a c; if, and only if, x is c, 'x is a satellite of the Earth' is true". This is an astronomical truth; but if you substitute "moon" or any other proper noun for "satellite of the earth," the end result is either meaningless or merely tautological."One" is therefore a property of certain concepts, just as "ten" is a property of the concept "my finger."But to argue "The earth has a satellite, the moon, therefore the moon is one" is as bad as to argue "The apostles are twelve, and Peter is an apostle; therefore Peter is twelve"; but if we take If "white" was substituted for "twelve," the argument would be valid. The above considerations show that, although there is one form of knowledge, namely, logic and mathematics, which is not derived from perception, Plato's arguments concerning all other knowledge are false.Of course, this does not prove that his conclusions are all false; it merely proves that Plato did not present valid reasons for assuming that his conclusions were true. (2) I come now to Protagoras' thesis that man is the measure of all things, or—as it is interpreted—every man is the measure of all things.The fundamental point here is that we must decide at what level the discussion takes place.Obviously, first we must distinguish perception from inference.In perception, a man is inevitably confined to his own perceptions; and whatever he knows of other people's perceptions, he knows by inference from his own perceptions of sight and hearing.The perceptions of dreamers and lunatics are, as perceptions, just like those of other people; the only objection to them is that, because of their extraordinary context, they are liable to fallacious inferences. .But what about inferences?Are they equally personal and private?In a sense, we have to admit that they are too.Whatever I believe must be due to some reason which enables me to believe it.It is true that my reason may be another man's assertion, and it may be perfectly justifiable,—for example, that I am a judge hearing evidence.But however Protagoras I may be, it is always reasonable for me to prefer the opinion of a narrator to my own for a set of images; Discovery, if I disagree with him at first, just a little more carefulness can prove him right.In this sense, I can admit that another person is wiser than I am.Protagoras' argument, properly interpreted, does not imply the opinion that I never err, but only that the evidence of my error must be presented to me.Judgment can be made on my past self as well as on other people.But all this presupposes that inferences, as opposed to perceptions, have some impersonal standard of correctness.If either of my inferences is as good as any other, the anarchy of knowledge that Plato deduces from Protagoras would in fact appear.So on this important point Plato seems to be right.But empiricists say that perception is the touchstone for testing the correctness of empirical data in inferences. (3) The doctrine of universal flux is distorted by Plato, and we can hardly imagine that anyone else has ever asserted the extreme form which Plato ascribed to it.For example, let us assume that the colors we see are constantly changing. The word "red" may be applied to many colors; but if we say "I see red," we have no reason to think that it should not be true for the whole time during which we say it.Plato arrived at his results by applying logical oppositions such as seeing and not seeing, knowing and not knowing, to the process of constant change.But these oppositions do not apply to the description of processes of this kind.Suppose that on a foggy day you watch a man walk past you down the road: he becomes increasingly blurred, until at last a point is when you are sure you cannot see him, but during There was also an intervening period of doubt and uncertainty.Logical oppositions are created for our convenience, but constant change requires a measuring instrument, a possibility that Plato ignores.Therefore, most of what he said on this subject was wrong. At the same time, we must admit that discussion is impossible unless words have a definite meaning within certain limits.Here, however, it is easy for us to be too absolute.The meaning of words is indeed changing, let us take the word "idea" as an example.It is only after a considerable education that we learn to ascribe to the word a meaning as Plato ascribed to it.It is necessary that changes in the meaning of words should lag behind the changes described by words; but it is not necessary that the meaning of words should not change.Perhaps this does not apply to the abstract words of logic and mathematics, which (we have seen) apply only to the form of propositions and not to their content.So here again we find that logic and mathematics are special.Plato was influenced by the Pythagoreans and overly assimilated other knowledge into mathematics.He made this mistake along with many of the greatest philosophers, but it was a mistake after all.