turns white, there will be white, but no black. Again, since the
fact that Socrates is ill is the contrary of the fact that
Socrates is well, and two contrary conditions cannot both obtain
in one and the same individual at the same time, both these
contraries could not exist at once: for if that Socrates was well
was a fact, then that Socrates was ill could not possibly be one.

It is plain that contrary attributes must needs be present in
subjects which belong to the same species or genus. Disease and
health 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.

Part 12

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