The Complete Aristotle (eng.)

of true and false. This depends, on the
side of the objects, on their being combined or separated, so that
he who thinks the separated to be separated and the combined to be
combined has the truth, while he whose thought is in a state
contrary to that of the objects is in error. This being so, when is
what is called truth or falsity present, and when is it not? We
must consider what we mean by these terms. It is not because we
think truly that you are pale, that you are pale, but because you
are pale we who say this have the truth. If, then, some things are
always combined and cannot be separated, and others are always
separated and cannot be combined, while others are capable either
of combination or of separation, ‘being’ is being combined and one,
and ‘not being’ is being not combined but more than one. Regarding
contingent facts, then, the same opinion or the same statement
comes to be false and true, and it is possible for it to be at one
time correct and at another erroneous; but regarding things that
cannot be otherwise opinions are not at one time true and at
another false, but the same opinions are always true or always
false.
    But with regard to incomposites, what is being or not being, and
truth or falsity? A thing of this sort is not composite, so as to
‘be’ when it is compounded, and not to ‘be’ if it is separated,
like ‘that the wood is white’ or ‘that the diagonal is
incommensurable’; nor will truth and falsity be still present in
the same way as in the previous cases. In fact, as truth is not the
same in these cases, so also being is not the same; but (a) truth
or falsity is as follows—contact and assertion are truth (assertion
not being the same as affirmation), and ignorance is non-contact.
For it is not possible to be in error regarding the question what a
thing is, save in an accidental sense; and the same holds good
regarding non-composite substances (for it is not possible to be in
error about them). And they all exist actually, not potentially;
for otherwise they would have come to be and ceased to be; but, as
it is, being itself does not come to be (nor cease to be); for if
it had done so it would have had to come out of something. About
the things, then, which are essences and actualities, it is not
possible to be in error, but only to know them or not to know them.
But we do inquire what they are, viz. whether they are of such and
such a nature or not.
    (b) As regards the ‘being’ that answers to truth and the
‘non-being’ that answers to falsity, in one case there is truth if
the subject and the attribute are really combined, and falsity if
they are not combined; in the other case, if the object is existent
it exists in a particular way, and if it does not exist in this way
does not exist at all. And truth means knowing these objects, and
falsity does not exist, nor error, but only ignorance-and not an
ignorance which is like blindness; for blindness is akin to a total
absence of the faculty of thinking.
    It is evident also that about unchangeable things there can be
no error in respect of time, if we assume them to be unchangeable.
E.g. if we suppose that the triangle does not change, we shall not
suppose that at one time its angles are equal to two right angles
while at another time they are not (for that would imply change).
It is possible, however, to suppose that one member of such a class
has a certain attribute and another has not; e.g. while we may
suppose that no even number is prime, we may suppose that some are
and some are not. But regarding a numerically single number not
even this form of error is possible; for we cannot in this case
suppose that one instance has an attribute and another has not, but
whether our judgement be true or false, it is implied that the fact
is eternal.

Book X
    Translated by W. D. Ross
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    div id="section109" class="section" title="1">
1
    We have said previously, in our distinction of the various
meanings of words, that ‘one’ has several meanings; the things that
are directly and of their own nature and not accidentally called
one may be summarized under four heads, though the word is used in
more senses. (1) There is the continuous, either in general, or
especially that which is continuous by nature and not by contact
nor by being together; and of these, that has more unity and is
prior, whose movement is more indivisible and simpler. (2) That
which is a whole and has a certain shape and form is one in a