From the same view proceeds the theory of Protagoras, and both alike must be either true or false. For if all opinions and appearances are true, everything must be at once true and false; for many people form judgements which are opposite to those of others, and imagine that those who do not think the same as themselves are wrong: hence the same thing must both be and not be. And if this is so, all opinions must be true; for those who are wrong and those who are right think contrarily to each other. So if reality is of this nature, everyone will be right. Clearly then both these theories proceed from the same mental outlook. But the method of approach is not the same for all cases; for some require persuasion and others compulsion. The ignorance of those who have formed this judgement through perplexity is easily remedied, because we are dealing not with the theory but with their mental outlook; but those who hold the theory for its own sake can only be cured by refuting the theory as expressed in their own speech and words. This view comes to those who are perplexed from their observation of sensible things. (1.) The belief that contradictions and contraries can be true at the same time comes to them from seeing the contraries generated from the same thing. Then if what is not cannot be generated, the thing must have existed before as both contraries equally—just as Anaxagoras says¹ that everything is mixed in everything; and also Democritus, for he too says² that Void and Plenum are present equally in any part, and yet the latter is , and the former is not. To those, then, who base their judgement on these considerations, we shall say that although in one sense their theory is correct, in another they are mistaken. For “being” has two meanings, so that there is a sense in which something can be generated from “not-being,” and a sense in which it cannot; and a sense in which the same thing can at once be and not be; but not in the same respect. For the same thing can “be” contraries at the same time potentially, but not actually. And further, we shall request them to conceive another kind also of substance of existing things, in which there is absolutely no motion or destruction or generation. 1009bAnd (2.) similarly the theory that there is truth in appearances has come to some people from an observation of sensible things. They think that the truth should not be judged by the number or fewness of its upholders; and they say that the same thing seems sweet to some who taste it, and bitter to others; so that if all men were diseased or all insane, except two or three who were healthy or sane, the latter would seem to be diseased or insane, and not the others. And further they say that many of the animals as well get from the same things impressions which are contrary to ours, and that the individual himself does not always think the same in matters of sense-perception. Thus it is uncertain which of these impressions are true or false; for one kind is no more true than another, but equally so. And hence Democritus says³ that either there is no truth or we cannot discover it. And in general it is because they suppose that thought is sense-perception, and sense-perception physical alteration, that they say that the impression given through sense-perception is necessarily true; for it is on these grounds that both Empedocles and Democritus and practically all the rest have become obsessed by such opinions as these. For Empedocles says that those who change their bodily condition change their thought: For according to that which is present to them doth thought increase in men.⁴ And in another passage he says: And as they change into a different nature, so it ever comes to them to think differently.⁵ And Parmenides too declares in the same way: For as each at any time hath the temperament of his many-jointed limbs, so thought comes to men. For for each and every man the substance of his limbs is that very thing which thinks; for thought is that which preponderates.⁶ There is also recorded a saying of Anaxagoras to some of his disciples, that things would be for them as they judged them to be. And they say that in Homer too clearly held this view, because he made Hector,⁷ when he was stunned by the blow, lie with thoughts deranged—thus implying that even those who are “out of their minds” still think, although not the same thoughts. Clearly then, if both are kinds of thought, reality also will be “both so and not so.” It is along this path that the consequences are most difficult; for if those who have the clearest vision of such truth as is possible (and these are they who seek and love it most) hold such opinions and make these pronouncements about the truth, surely those who are trying to be philosophers may well despair; for the pursuit of truth will be “chasing birds in the air.” ⁸ 1010aBut the reason why these men hold this view is that although they studied the truth about reality, they supposed that reality is confined to sensible things, in which the nature of the Indeterminate, i.e. of Being in the sense which we have explained,⁹ is abundantly present. (Thus their statements, though plausible, are not true; this form of the criticism is more suitable than that which Epicharmus¹⁰ applied to Xenophanes.) And further, observing that all this indeterminate substance is in motion, and that no true predication can be made of that which changes, they supposed that it is impossible to make any true statement about that which is in all ways and entirely changeable. For it was from this supposition that there blossomed forth the most extreme view of those which we have mentioned, that of the professed followers of Heraclitus, and such as Cratylus held, who ended by thinking that one need not say anything, and only moved his finger; and who criticized Heraclitus for saying that one cannot enter the same river twice,¹¹ for he himself held that it cannot be done even once. But we shall reply to this theory also that although that which is changeable supplies them, when it changes, with some real ground for supposing that it “is not,” yet there is something debatable in this; for that which is shedding any quality retains something of that which is being shed, and something of that which is coming to be must already exist. And in general if a thing is ceasing to be, there will be something there which is ; and if a thing is coming to be, that from which it comes and by which it is generated must be ; and this cannot go on to infinity. But let us leave this line of argument and remark that quantitative and qualitative change are not the same. Let it be granted that there is nothing permanent in respect of quantity; but it is by the form that we recognize everything. And again those who hold the theory that we are attacking deserve censure in that they have maintained about the whole material universe what they have observed in the case of a mere minority of sensible things. For it is only the realm of sense around us which continues subject to destruction and generation, but this is a practically negligible part of the whole; so that it would have been fairer for them to acquit the former on the ground of the latter than to condemn the latter on account of the former. Further, we shall obviously say to these thinkers too the same as we said some time ago¹²; for we must prove to them and convince them that there is a kind of nature that is not moved (and yet those who claim that things can at once be and not be are logically compelled to admit rather that all things are at rest than that they are in motion; for there is nothing for them to change into, since everything exists in everything). 1010bAnd as concerning reality, that not every appearance is real, we shall say, first, that indeed the perception, at least of the proper object of a sense, is not false, but the impression we get of it is not the same as the perception. And then we may fairly express surprise if our opponents raise the question whether magnitudes and colors are really such as they appear at a distance or close at hand, as they appear to the healthy or to the diseased; and whether heavy things are as they appear to the weak or to the strong; and whether truth is as it appears to the waking or to the sleeping. For clearly they do not really believe the latter alternative—at any rate no one, if in the night he thinks that he is at Athens whereas he is really in Africa, starts off to the Odeum.¹³ And again concerning the future (as indeed Plato says¹⁴) the opinion of the doctor and that of the layman are presumably not equally reliable, e.g. as to whether a man will get well or not. And again in the case of the senses themselves, our perception of a foreign object and of an object proper to a given sense, or of a kindred object and of an actual object of that sense itself, is not equally reliable¹⁵; but in the case of colors sight, and not taste, is authoritative, and in the case of flavor taste, and not sight. But not one of the senses ever asserts at the same time of the same object that it is “so and not so.” Nor even at another time does it make a conflicting statement about the quality, but only about that to which the quality belongs. I mean, e.g., that the same wine may seem, as the result of its own change or of that of one’s body, at one time sweet and at another not; but sweetness, such as it is when it exists, has never yet changed, and there is no mistake about it, and that which is to be sweet is necessarily of such a nature. Yet all these theories destroy the possibility of anything’s existing by necessity, inasmuch as they destroy the existence of its essence; for “the necessary” cannot be in one way and in another; and so if anything exists of necessity, it cannot be “both so and not so.” And in general, if only the sensible exists, without animate things there would be nothing; for there would be no sense-faculty. That there would be neither sensible qualities nor sensations is probably true¹⁶(for these depend upon an effect produced in the percipient), but that the substrates which cause the sensation should not exist even apart from the sensation is impossible. For sensation is not of itself, but there is something else too besides the sensation, which must be prior to the sensation; 1011abecause that which moves is by nature prior to that which is moved, and this is no less true if the terms are correlative.