For the emotional and
unreasoning elements are subject to motions sometimes too quick and
vehement, at other times too remiss and slow. And so everything we do
may be a success from one point of view, but a failure from many points
of view; as to hit the mark one thing only is requisite, but one may
miss it in various ways, as one may shoot beyond or too short. This then
is the function of practical reason following nature, to prevent our
passions going either too far or too short. For where from weakness and
want of strength, or from fear and hesitation, the impetus gives in and
abandons what is good, there reason is by to stir it up and rekindle it;
and where on the other hand it goes ahead too fast and in disorder,
there it represses and checks its zeal. And thus setting bounds to the
emotional motions, it engenders in the unreasoning part of the soul
moral virtues, which are the mean between excess and deficiency. Not
that we can say that all virtue exists in the mean, but knowledge and
prudence being in no need of the unreasoning element, and being situated
in the pure and unemotional part of the soul, is a complete perfection
and power of reason, whereby we get the most divine and happy fruit of
understanding. But that virtue which is necessary because of the body,
and needs the help of the passions as an instrument towards the
practical, not destroying or doing away with but ordering and regulating
the unreasoning part of the soul, is perfection as regards its power and
quality, but in quantity it is a mean correcting both excess and
deficiency.

Sec. VI. But since the word mean has a variety of meanings--for there is
one kind of mean compounded of two simple extremes, as grey is the mean
between white and black; and there is another kind of mean, where that
which contains and is contained is the mean between the containing and
contained, as eight is the mean between twelve and four; and there is a
third kind of mean which has part in neither extreme, as the indifferent
is the mean between good and bad,--virtue cannot be a mean in any of
these ways. For neither is it a mixture of vices, nor containing that
which is defective is it contained by that which is excessive, nor is it
again altogether free from, emotional storms of passion, wherein are
excess and deficiency. But it is, and is commonly so called, a mean like
that in music and harmony. For as in music there is a middle note
between the highest and lowest