Part 10 (continued)
Neither in the case of contraries, nor in the case of
correlatives, nor in the case of 'positives' and '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.