negation belong manifestly to a class which is distinct, for in this
case, and in this case only, it is necessary for the one opposite to
be true and the other false.
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
But in the case of affirmation and negation, whether the subject