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 reversed. In this sense ‘one’ is ‘prior’ to
‘two’. For if ‘two’ exists, it follows directly that ‘one’ must exist,
but if ‘one’ exists, it does not follow necessarily that ‘two’ exists:
thus the sequence subsisting cannot be reversed. It is agreed, then,
that when the sequence of two things cannot be reversed, then that one
on which the other depends is called ‘prior’ to that other.
In the third place, the term ‘prior’ is used with reference to any
order, as in the case of science and of oratory. For in sciences which
use demonstration there is that which is prior and that which is
posterior in order; in geometry, the elements are prior to the
propositions; in reading and writing, the letters of the alphabet are
prior to the syllables. Similarly, in the case of speeches, the
exordium is prior in order to the narrative.
Besides these senses of the word, there is a fourth. That which is
better and more honourable is said to have a natural priority. In
common parlance men speak of those whom they honour and love as ‘coming
first’ with them. This sense of the word is perhaps the most
Such, then, are the different senses in which the term ‘prior’ is used.
Yet it would seem that besides those mentioned there is yet another.
For in those things, the being of each of which implies that of the
other, that which is in any way the cause may reasonably be said to be
by nature ‘prior’ to the effect. It is plain that there are instances
of this. The fact of the being of a man carries with it the truth of
the proposition that he is, and the implication is reciprocal: for if a
man is, the proposition wherein we allege that he is true, and
conversely, if the proposition wherein we allege that he is true, then
he is. The true proposition, however, is in no way the cause of the
being of the man, but the fact of the man’s being does seem somehow to
be the cause of the truth of the proposition, for the truth or falsity
of the proposition depends on the fact of the man’s being or not being.
Thus the word ‘prior’ may be used in five senses.