But what general characteristics distinguish right acts and right habits from wrong ones? Aristotle is guided in answering the question by an analogy which is really at the bottom of all Greek thinking on morality. The thought is that goodness is in the soul what health and fitness are in the body, and that the preceptor is for the soul what the physician or the trainer is for the body. Now it was a well-known medical theory, favoured by both Plato and Aristotle, that health in the body means a condition of balance or equilibration among the elements of which it is composed. When the hot and the cold, the moist and the dry in the composition of the human frame exactly balance one another, the body is in perfect health. Hence the object of the regimen of the physician or the trainer is to produce and maintain a proper balance or proportion between the ingredients of the body. Any course which disturbs this balance is injurious to health and strength. You damage your health if you take too much food or exercise, and also if you take too little. The same thing is true of health in the soul. Our soul’s health may be injured by allowing too much or too little play to any of our natural impulses or feelings. We may lay it down, then, that the kind of training which gives rise to a good habit is training in the avoidance of the opposite errors of the too much and the too little. And since the effect of training is to produce habits which issue in the spontaneous performance of the same kind of acts by which the habits were acquired, we may say not merely that goodness of character is produced by acts which exhibit a proper balance or mean, but that it is a settled habit of acting so as to exhibit the same balance or proportion. Hence the formal definition of goodness of character is that it is "a settled condition of the soul which wills or chooses the mean relatively to ourselves, this mean being determined by a rule or whatever we like to call that by which the wise man determines it."