We may perhaps state that necessity and its absence are the
initial principles of existence and non-existence, and that all else
must be regarded as posterior to these.
It is plain from what has been said that that which is of
necessity is actual. Thus, if that which is eternal is prior,
actuality also is prior to potentiality. Some things are actualities
without potentiality, namely, the primary substances; a second class
consists of those things which are actual but also potential, whose
actuality is in nature prior to their potentiality, though posterior
in time; a third class comprises those things which are never
actualized, but are pure potentialities.
The question arises whether an affirmation finds its contrary in a
denial or in another affirmation; whether the proposition 'every man
is just' finds its contrary in the proposition 'no man is just', or in
the proposition 'every man is unjust'. Take the propositions
'Callias is just', 'Callias is not just', 'Callias is unjust'; we have
to discover which of these form contraries.
Now if the spoken word corresponds with the judgement of the mind,
and if, in thought, that judgement is the contrary of another, which
pronounces a contrary fact, in the way, for instance, in which the
judgement 'every man is just' pronounces a contrary to that pronounced
by the judgement 'every man is unjust', the same must needs hold
good with regard to spoken affirmations.
But if, in thought, it is not the judgement which pronounces a
contrary fact that is the contrary of another, then one affirmation
will not find its contrary in another, but rather in the corresponding
denial. We must therefore consider which true judgement is the
contrary of the false, that which forms the denial of the false
judgement or that which affirms the contrary fact.
Let me illustrate. There is a true judgement concerning that which