The Complete Aristotle (eng.)

nature; for nothing that exists by
nature can form a habit contrary to its nature. For instance the
stone which by nature moves downwards cannot be habituated to move
upwards, not even if one tries to train it by throwing it up ten
thousand times; nor can fire be habituated to move downwards, nor
can anything else that by nature behaves in one way be trained to
behave in another. Neither by nature, then, nor contrary to nature
do the virtues arise in us; rather we are adapted by nature to
receive them, and are made perfect by habit.
    Again, of all the things that come to us by nature we first
acquire the potentiality and later exhibit the activity (this is
plain in the case of the senses; for it was not by often seeing or
often hearing that we got these senses, but on the contrary we had
them before we used them, and did not come to have them by using
them); but the virtues we get by first exercising them, as also
happens in the case of the arts as well. For the things we have to
learn before we can do them, we learn by doing them, e.g. men
become builders by building and lyreplayers by playing the lyre; so
too we become just by doing just acts, temperate by doing temperate
acts, brave by doing brave acts.
    This is confirmed by what happens in states; for legislators
make the citizens good by forming habits in them, and this is the
wish of every legislator, and those who do not effect it miss their
mark, and it is in this that a good constitution differs from a bad
one.
    Again, it is from the same causes and by the same means that
every virtue is both produced and destroyed, and similarly every
art; for it is from playing the lyre that both good and bad
lyre-players are produced. And the corresponding statement is true
of builders and of all the rest; men will be good or bad builders
as a result of building well or badly. For if this were not so,
there would have been no need of a teacher, but all men would have
been born good or bad at their craft. This, then, is the case with
the virtues also; by doing the acts that we do in our transactions
with other men we become just or unjust, and by doing the acts that
we do in the presence of danger, and being habituated to feel fear
or confidence, we become brave or cowardly. The same is true of
appetites and feelings of anger; some men become temperate and
good-tempered, others self-indulgent and irascible, by behaving in
one way or the other in the appropriate circumstances. Thus, in one
word, states of character arise out of like activities. This is why
the activities we exhibit must be of a certain kind; it is because
the states of character correspond to the differences between
these. It makes no small difference, then, whether we form habits
of one kind or of another from our very youth; it makes a very
great difference, or rather all the difference.
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2
    Since, then, the present inquiry does not aim at theoretical
knowledge like the others (for we are inquiring not in order to
know what virtue is, but in order to become good, since otherwise
our inquiry would have been of no use), we must examine the nature
of actions, namely how we ought to do them; for these determine
also the nature of the states of character that are produced, as we
have said. Now, that we must act according to the right rule is a
common principle and must be assumed-it will be discussed later,
i.e. both what the right rule is, and how it is related to the
other virtues. But this must be agreed upon beforehand, that the
whole account of matters of conduct must be given in outline and
not precisely, as we said at the very beginning that the accounts
we demand must be in accordance with the subject-matter; matters
concerned with conduct and questions of what is good for us have no
fixity, any more than matters of health. The general account being
of this nature, the account of particular cases is yet more lacking
in exactness; for they do not fall under any art or precept but the
agents themselves must in each case consider what is appropriate to
the occasion, as happens also in the art of medicine or of
navigation.
    But though our present account is of this nature we must give
what help we can. First, then, let us consider this, that it is the
nature of such things to be destroyed by defect and excess, as we
see in the case of strength and of health (for to gain light on
things imperceptible we must use the evidence of sensible things);
both excessive and defective