Metaphysics

​And even if things here are continually flowing and moving in respect of quantity, and even if someone should assume this although it is not true, why should they not remain constant in respect of quality? For it seems that they assert contradictory things of the same object not least because they have assumed that quantity does not remain constant in bodies, and therefore that the same thing both is four cubits long and is not. But substance depends on quality, and this belongs to a determinate nature, whereas quantity belongs to an indeterminate nature. Furthermore, when the doctor orders them to take this food, why do they take it? For why is this rather bread than not? So it would make no difference whether they eat it or not; but as it is, they take it as though they were speaking the truth about it and as though this were indeed the food ordered. Yet they ought not to do so if no nature remains constant in sensible things, but all are always moving and flowing. Furthermore, if we are always changing qualitatively and never remain the same, what wonder is it if things never appear the same to us, just as is the case with those who are sick? (For to these, because their disposition is not in the same state as when they were healthy, things presented to their senses do not appear the same, though the sensible things themselves do not share in any change on this account, but produce different and not the same sensations in those who are sick; and in the same way, surely, it must also be if the aforementioned change takes place.) But if we do not change, but continue being the same, there must be something that remains constant. — Now, as for those who have the aforementioned difficulties because of an argument, it is not easy to resolve them unless they posit something and no longer demand a reason for this; for it is in this way that every argument and every demonstration comes to be; for by positing nothing they destroy discussion and argument altogether. Hence, with such people there is no argument, but as for those who are in doubt because of the difficulties handed down, it is easy to meet them and resolve the causes of their difficulty. This is clear from what has been said. Thus, it is manifest from these things that contradictory assertions cannot be true of the same thing at one time, nor can contraries, because every contrariety is stated in terms of privation; and this is clear to those who analyze the definitions of contraries back to their origin. Likewise, no intermediate can be predicated of one and the same thing. For if the subject is white, we shall speak falsely if we say it is neither black nor white; for it follows that it is both white and not white, since one of the two combined assertions will be true of it, and this is the contradiction of white. It is, therefore, impossible for those who speak according to Heraclitus to speak the truth, nor according to Anaxagoras; otherwise, it will follow that contraries are predicated of the same thing. For when he says that in everything there is a portion of everything, he says that it is no more sweet than bitter, or than any of the other contrarieties, if indeed everything is present in everything, not potentially only, but actually and distinctly. Likewise, it is not possible that all assertions are false, nor that all are true, both because of many other difficulties that would follow from this position, and because if all are false, even the one who asserts this very thing will not be speaking the truth, and if all are true, the one who says that all are false will not be speaking falsely.