require as their subject the body of an animal; white and black
require a body, without further qualification; justice and injustice
require as their subject the human soul.
Moreover, it is necessary that pairs of contraries should in all
cases either belong to the same genus or belong to contrary genera
or be themselves genera. White and black belong to the same genus,
colour; justice and injustice, to contrary genera, virtue and vice;
while good and evil do not belong to genera, but are themselves actual
genera, with terms under them.
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