The Complete Aristotle (eng.)

that which can do so in
another—the contrary—way is vicious. Good and evil indicate quality
especially in living things, and among these especially in those
which have purpose.
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15
    Things are ‘relative’ (1) as double to half, and treble to a
third, and in general that which contains something else many times
to that which is contained many times in something else, and that
which exceeds to that which is exceeded; (2) as that which can heat
to that which can be heated, and that which can cut to that which
can be cut, and in general the active to the passive; (3) as the
measurable to the measure, and the knowable to knowledge, and the
perceptible to perception.
    (1) Relative terms of the first kind are numerically related
either indefinitely or definitely, to numbers themselves or to 1.
E.g. the double is in a definite numerical relation to 1, and that
which is ‘many times as great’ is in a numerical, but not a
definite, relation to 1, i.e. not in this or in that numerical
relation to it; the relation of that which is half as big again as
something else to that something is a definite numerical relation
to a number; that which is n+I/n times something else is in an
indefinite relation to that something, as that which is ‘many times
as great’ is in an indefinite relation to 1; the relation of that
which exceeds to that which is exceeded is numerically quite
indefinite; for number is always commensurate, and ‘number’ is not
predicated of that which is not commensurate, but that which
exceeds is, in relation to that which is exceeded, so much and
something more; and this something is indefinite; for it can,
indifferently, be either equal or not equal to that which is
exceeded.-All these relations, then, are numerically expressed and
are determinations of number, and so in another way are the equal
and the like and the same. For all refer to unity. Those things are
the same whose substance is one; those are like whose quality is
one; those are equal whose quantity is one; and 1 is the beginning
and measure of number, so that all these relations imply number,
though not in the same way.
    (2) Things that are active or passive imply an active or a
passive potency and the actualizations of the potencies; e.g. that
which is capable of heating is related to that which is capable of
being heated, because it can heat it, and, again, that which heats
is related to that which is heated and that which cuts to that
which is cut, in the sense that they actually do these things. But
numerical relations are not actualized except in the sense which
has been elsewhere stated; actualizations in the sense of movement
they have not. Of relations which imply potency some further imply
particular periods of time, e.g. that which has made is relative to
that which has been made, and that which will make to that which
will be made. For it is in this way that a father is called the
father of his son; for the one has acted and the other has been
acted on in a certain way. Further, some relative terms imply
privation of potency, i.e. ‘incapable’ and terms of this sort, e.g.
‘invisible’.
    Relative terms which imply number or potency, therefore, are all
relative because their very essence includes in its nature a
reference to something else, not because something else involves a
reference to it; but (3) that which is measurable or knowable or
thinkable is called relative because something else involves a
reference to it. For ‘that which is thinkable’ implies that the
thought of it is possible, but the thought is not relative to ‘that
of which it is the thought’; for we should then have said the same
thing twice. Similarly sight is the sight of something, not ‘of
that of which it is the sight’ (though of course it is true to say
this); in fact it is relative to colour or to something else of the
sort. But according to the other way of speaking the same thing
would be said twice,-’the sight is of that of which it is.’
    Things that are by their own nature called relative are called
so sometimes in these senses, sometimes if the classes that include
them are of this sort; e.g. medicine is a relative term because its
genus, science, is thought to be a relative term. Further, there
are the properties in virtue of which the things that have them are
called relative, e.g. equality is relative because the equal is,
and likeness because the like is. Other things are