psychology, in part by analogies suggested by art and nature,
and in part by criteria elaborated by the intellectual virtues.
The genus of the moral virtues is determined by a dialectical
choice among the three things in the soul: they are not passions
or faculties but habits. Their differentia is determined in
two fashions, relative to the person of the agent and relative
to rational criteria. For the first, Aristotle draws an analogy
from natural and artistic excellence to moral excellence, inferring
that virtue as habit disposes one to choose in the right way
among actions and passions, and that the right way involves a
mean between extremes. Such a mean proportion may be determined
in action by habit without explicit knowledge, but if
it is to be stated it is made a rational rule and therefore subject
in its second formulation to an intellectual virtue. The final
definition therefore bears only a dialectical likness to a scientific
definition by genus and differentia: "Virtue, then, is a habit
concerned with choice (6"ls wpoaLpErLK), lying in a mean, i.e.,
the mean relative to us, this being determined by a rational
principle, and by that principle by which the prudent man
would determine it."24 In its construction the four causes, which
are important also in determining the methods of metaphysics
and physics, are all discernible. Physical definitions usually
specify two of the causes, the matter and some formal determination
of the matter.25 The virtues, however, are not themselves
actions but are oriented to actions: the genus of virtue
is therefore found in the efficient cause of actions, namely, habit
concerned with choice, and the differentia supplies the criteria
for such actions tated eitheri n the formalc onsiderationos f a proportion
or in the final determinationso f a rational rule. Moreover,
this definition of the moral virtues in turn serves as a
genus,26a nd furthers pecificationsa re made by introducingi nto
the proportion the material causes-i.e., the passions and actions
with which the virtues are concer