Chapter XX. Against the School of Metrodorus and Protagoras, Who Say That the Senses Alone Are to Be Trusted. From the Same

‘Now there have been men who maintained that we must believe only sense and its presentations. Some indeed say that even Homer intimates this kind of doctrine by declaring that Ocean is the first principle, as though all things were in flux. But of those known to us, Metrodorus of Chios seems to make the same statement; Protagoras of Abdera not only seems, but expressly states this.

‘For he said that “the Man is the measure of all things, of existing things, that they exist, of non-existent things, that they do not exist: for as things appear to each person, such they also are; and of the rest we can affirm nothing positively.”

‘Now in answer to them one may say what Plato says in the Theaetetus:[1]in the first place, why in the world, if such forsooth is the nature of things, did he assert that “the Man” is the measure of truth and not a pig or a dog-headed ape? But next, how did they mean that themselves were wise, if forsooth every one is the measure of truth to himself? Or how do they refute other men, if that which appears to each is true? And how is it that we are ignorant of some things, though we often perceive them by sensation, just as when we hear barbarians speaking?

‘Moreover the man who has seen anything, and then remembers it, knows it, though he is no longer sensible of it. And if he should shut one eye and see with the other, he will evidently be both knowing and not knowing the same thing.

‘And in addition to this, if that which appears to each is also true, but what they say does not appear true to us, it must also be true that the Man is not the measure of all things.

‘Moreover artists are superior to the unskilled, and experts to the inexperienced, and for this reason a pilot, or a physician, or a general foresees better what is about to happen.

‘These men too absolutely destroy the degrees of the more or less, and the necessary and contingent, and the natural and unnatural. And thus the same thing would both be and not be; for nothing hinders the same thing from appearing to some to be, and to others not to be. And the same thing would be both a man and a block: for sometimes the same thing appears to one a man and to another a block.

‘Every speech too would be true, but also for this reason false: and counsellors and judges would not have anything to do. And what is most terrible, the same persons will be both good and bad, and vice and virtue the same thing. Many other instances also of this kind one might mention; but in fact there is no need of more arguments against those who think that they have no mind nor reason.’

Then next he adds:

‘But since there are even now some who say that every sensation and every presentation is true, let us say a few words about them also. For these seem to be afraid lest, if they should say that some sensations are false, they should not have their criterion and their canon sure and trustworthy: but they fail to see that, if this be so, they should lose no time in declaring that all opinions also are true; for it is natural to us to judge by them also of many things: and nevertheless they maintain that some opinions are true and some false.

‘And then if one were to examine he would see that none even of the other criteria are always and thoroughly free from error; as for instance I mean a balance, or a turning-lathe, or anything of this kind: but each of them in one condition is sound and in another bad; and when men use it in this way, it tells true, but in that way tells false. Moreover if every sensation were true, they ought not to differ so much. For they are different when near and far off, and in the sick and the strong, and in the skilled and unskilled, and prudent and senseless. And of course it would be altogether absurd to say that the sensations of the mad are true, and of those who see amiss, and hear amiss. For the statement that he who sees amiss either sees or does not see would be silly: for one would answer, that he sees indeed, but not aright.

‘When, however, they say that sensation being devoid of reason neither adds anything nor takes away, it is evident that they fail to see the obstacles: for in the case of the oar in the water, and in pictures, and numberless other things, it is the sense that deceives. Wherefore in such cases we all lay the blame not on our mind, but on the presentation: for the argument refutes itself when it maintains that every presentation is true. For at all events it declares the falsity of ours, which causes us to think that not every presentation is true. The result then for them is to say that every presentation is both true and false.

‘And they are altogether wrong in maintaining that things really are just such as they may seem to us: for on the contrary they appear such as they are by nature, and we do not make them to be so, but are ourselves affected in a certain way by them. Since if we were to imagine puppies or young kids, as painters and sculptors do, it would be ridiculous to assert straightway that they existed, and therefore to represent them to ourselves as standing ready at hand.’

From what has been said then it is evident that they do not speak rightly who assert that every sensation and every presentation is true. But in fact, though this is so, Epicurus again, starting from the School of Aristippus, made all things depend on pleasure and sense, defining the feelings alone to be conceptional, and pleasure the end of all good.

Now some say that Epicurus had no teacher, but read the writings of the ancients; others say that he was a hearer of Xenocrates, and afterwards of Nausiphanes also, who had been a disciple of Pyrrho. Let us see then what are the arguments which have been urged against him also. [2]