thought, may make some advance, however slight, and if he
should once improve, even ever so little, it is plain that he might
change completely, or at any rate make very great progress; for a man
becomes more and more easily moved to virtue, however small the
improvement was at first. It is, therefore, natural to suppose that he
will make yet greater progress than he has made in the past; and as
this process goes on, it will change him completely and establish him
in the contrary state, provided he is not hindered by lack of time. In
the case of 'positives' and 'privatives', however, change in both
directions is impossible. There may be a change from possession to
privation, but not from privation to possession. The man who has become
blind does not regain his sight; the man who has become bald does not
regain his hair; the man who has lost his teeth does not grow a new
set. (iv) Statements opposed as affirmation and 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