Whereas intellectual excellence is chiefly generated and improved by teaching, moral excellence is a result of habit [Greek: ethos]; whence its name (Ethical). Hence we may see that moral excellence is no inherent part of our nature: if it were, it could not be reversed by habit--any more than a stone can acquire from any number of repetitions the habit of moving upward, or fire the habit of moving downward. These moral excellencies are neither a part of our nature, nor yet contrary to our nature: we are by nature fitted to take them on, but they are brought to consummation through habit. It is not with them, as with our senses, where nature first gives us the power to see and hear, and where we afterwards exercise that power. Moral virtues are acquired only by practice. We learn to build or to play the harp, by building or playing the harp: so too we become just or courageous, by a course of just or courageous acts. This is attested by all lawgivers in their respective cities; all of them shape the characters of their respective citizens, by enforcing habitual practice. Some do it well; others ill; according to the practice, so will be the resulting character; as he that is practised in building badly, will be a bad builder in the end; and he that begins on a bad habit of playing the harp, becomes confirmed into a bad player. Hence the importance of making the young perform good actions habitually and from the beginning. The permanent ethical acquirements are generated by uniform and persistent practice (I.). [This is the earliest statement of the philosophy of _habit_.] 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.).