The Complete Aristotle (eng.)

‘privatives’, is
it necessary for one to be true and the other false. Health and
disease are contraries: neither of them is true or false. ‘Double’
and ‘half’ are opposed to each other as correlatives: neither of
them is true or false. The case is the same, of course, with regard
to ‘positives’ and ‘privatives’ such as ‘sight’ and ‘blindness’. In
short, where there is no sort of combination of words, truth and
falsity have no place, and all the opposites we have mentioned so
far consist of simple words.
    At the same time, when the words which enter into opposed
statements are contraries, these, more than any other set of
opposites, would seem to claim this characteristic. ‘Socrates is
ill’ is the contrary of ‘Socrates is well’, but not even of such
composite expressions is it true to say that one of the pair must
always be true and the other false. For if Socrates exists, one
will be true and the other false, but if he does not exist, both
will be false; for neither ‘Socrates is ill’ nor ‘Socrates is well’
is true, if Socrates does not exist at all.
    In the case of ‘positives’ and ‘privatives’, if the subject does
not exist at all, neither proposition is true, but even if the
subject exists, it is not always the fact that one is true and the
other false. For ‘Socrates has sight’ is the opposite of ‘Socrates
is blind’ in the sense of the word ‘opposite’ which applies to
possession and privation. Now if Socrates exists, it is not
necessary that one should be true and the other false, for when he
is not yet able to acquire the power of vision, both are false, as
also if Socrates is altogether non-existent.
    But in the case of affirmation and negation, whether the subject
exists or not, one is always false and the other true. For
manifestly, if Socrates exists, one of the two propositions
‘Socrates is ill’, ‘Socrates is not ill’, is true, and the other
false. This is likewise the case if he does not exist; for if he
does not exist, to say that he is ill is false, to say that he is
not ill is true. Thus it is in the case of those opposites only,
which are opposite in the sense in which the term is used with
reference to affirmation and negation, that the rule holds good,
that one of the pair must be true and the other false.
11
    That the contrary of a good is an evil is shown by induction:
the contrary of health is disease, of courage, cowardice, and so
on. But the contrary of an evil is sometimes a good, sometimes an
evil. For defect, which is an evil, has excess for its contrary,
this also being an evil, and the mean. which is a good, is equally
the contrary of the one and of the other. It is only in a few
cases, however, that we see instances of this: in most, the
contrary of an evil is a good.
    In the case of contraries, it is not always necessary that if
one exists the other should also exist: for if all become healthy
there will be health and no disease, and again, if everything turns
white, there will be white, but no black. Again, since the fact
that Socrates is ill is the contrary of the fact that Socrates is
well, and two contrary conditions cannot both obtain in one and the
same individual at the same time, both these contraries could not
exist at once: for if that Socrates was well was a fact, then that
Socrates was ill could not possibly be one.
    It is plain that contrary attributes must needs be present in
subjects which belong to the same species or genus. Disease and
health require as their subject the body of an animal; white and
black require a body, without further qualification; justice and
injustice require as their subject the human soul.
    Moreover, it is necessary that pairs of contraries should in all
cases either belong to the same genus or belong to contrary genera
or be themselves genera. White and black belong to the same genus,
colour; justice and injustice, to contrary genera, virtue and vice;
while good and evil do not belong to genera, but are themselves
actual genera, with terms under them.
12
    There are four senses in which one thing can be said to be
‘prior’ to another. Primarily and most properly the term has
reference to time: in this sense the word is used to indicate that
one thing is older or more ancient than another, for the
expressions ‘older’ and ‘more ancient’ imply greater length of
time.
    Secondly, one thing is said to be ‘prior’ to another when the
sequence of their being cannot be