Everything thus turns upon practice: and Aristotle reminds us that his

purpose here is, not simply to teach what virtue is, but to produce
virtuous agents
Everything thus turns upon practice: and Aristotle reminds us that his
purpose here is, not simply to teach what virtue is, but to produce
virtuous agents. How are we to know what the practice should be? It
must be conformable to right reason: every one admits this, and we
shall explain it further in a future book. But let us proclaim at
once, that in regard to moral action, as in regard to health, no exact
rules can be laid down. Amidst perpetual variability, each agent must
in the last resort be guided by the circumstances of the case. Still,
however, something may be done to help him. Here Aristotle proceeds to
introduce the famous doctrine of the MEAN. We may err, as regards
health, both by too much and by too little of exercise, food, or
drink. The same holds good in regard to temperance, courage, and the
other excellences (II.).