The Complete Aristotle (eng.)

same and share in no change.
    Further, if there is movement, there is also something moved,
and everything is moved out of something and into something; it
follows that that that which is moved must first be in that out of
which it is to be moved, and then not be in it, and move into the
other and come to be in it, and that the contradictory statements
are not true at the same time, as these thinkers assert they
are.
    And if the things of this earth continuously flow and move in
respect of quantity-if one were to suppose this, although it is not
true-why should they not endure in respect of quality? For the
assertion of contradictory statements about the same thing seems to
have arisen largely from the belief that the quantity of bodies
does not endure, which, our opponents hold, justifies them in
saying that the same thing both is and is not four cubits long. But
essence depends on quality, and this is of determinate nature,
though quantity is of indeterminate.
    Further, when the doctor orders people to take some particular
food, why do they take it? In what respect is ‘this is bread’ truer
than ‘this is not bread’? And so it would make no difference
whether one ate or not. But as a matter of fact they take the food
which is ordered, assuming that they know the truth about it and
that it is bread. Yet they should not, if there were no fixed
constant nature in sensible things, but all natures moved and
flowed for ever.
    Again, if we are always changing and never remain the same, what
wonder is it if to us, as to the sick, things never appear the
same? (For to them also, because they are not in the same condition
as when they were well, sensible qualities do not appear alike;
yet, for all that, the sensible things themselves need not share in
any change, though they produce different, and not identical,
sensations in the sick. And the same must surely happen to the
healthy if the afore-said change takes place.) But if we do not
change but remain the same, there will be something that
endures.
    As for those to whom the difficulties mentioned are suggested by
reasoning, it is not easy to solve the difficulties to their
satisfaction, unless they will posit something and no longer demand
a reason for it; for it is only thus that all reasoning and all
proof is accomplished; if they posit nothing, they destroy
discussion and all reasoning. Therefore with such men there is no
reasoning. But as for those who are perplexed by the traditional
difficulties, it is easy to meet them and to dissipate the causes
of their perplexity. This is evident from what has been said.
    It is manifest, therefore, from these arguments that
contradictory statements cannot be truly made about the same
subject at one time, nor can contrary statements, because every
contrariety depends on privation. This is evident if we reduce the
definitions of contraries to their principle.
    Similarly, no intermediate between contraries can be predicated
of one and the same subject, of which one of the contraries is
predicated. If the subject is white we shall be wrong in saying it
is neither black nor white, for then it follows that it is and is
not white; for the second of the two terms we have put together is
true of it, and this is the contradictory of white.
    We could not be right, then, in accepting the views either of
Heraclitus or of Anaxagoras. If we were, it would follow that
contraries would be predicated of the same subject; for when
Anaxagoras says that in everything there is a part of everything,
he says nothing is sweet any more than it is bitter, and so with
any other pair of contraries, since in everything everything is
present not potentially only, but actually and separately. And
similarly all statements cannot be false nor all true, both because
of many other difficulties which might be adduced as arising from
this position, and because if all are false it will not be true to
say even this, and if all are true it will not be false to say all
are false.
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7
    Every science seeks certain principles and causes for each of
its objects-e.g. medicine and gymnastics and each of the other
sciences, whether productive or mathematical. For each of these
marks off a certain class of things for itself and busies itself
about this as about something existing and real,-not however qua
real; the science that does this is another distinct from these. Of
the sciences mentioned each gets somehow the