In addition to the endless diversities that result from these varied proportions and combinations, there is a manifest variety in the grades of mind. Some races are much lower in the scale of being every way than others, while the same disparity exists in individuals of the same race. The wisdom and benevolence of this arrangement is very manifest when viewed in reference to the interests of a commonwealth. Where some must lead and others follow, it is well that some have the love of power strong, and others have it less. Where some must be rulers, to inflict penalties as well as to apportion rewards, it is well that there be some who have the sense of justice a leading principle. And so in the developments of intellect. Some men are to follow callings where the reasoning powers are most needed. Others are to adopt pursuits in which taste and imagination are chiefly required; and thus the varied proportions of these faculties become serviceable. And if it be true that the exercise of the social and moral faculties secures the highest degrees of enjoyment, those disparities in mental powers which give exercise to the virtues of compassion, self-denial, fortitude, and benevolence in serving the weak, and the corresponding exercises of gratitude, reverence, humility, and devotion in those who are thus benefited, then we can see the wisdom and benevolence of this gradation of mental capacity. Moreover, in a commonwealth perfectly organized, where the happiness of the whole becomes that of each part, whatever tends to the highest general good tends to the best interest of each individual member. This being so, the lowest and humblest in the scale of being, in his appropriate place, is happier than he could be by any other arrangement, and happier than he could be if all were equally endowed. CHAPTER XXI. HABIT. Habit is a facility in performing physical or mental operations, gained by the repetition of such acts. As examples of this in _physical_ operations may be mentioned the power of walking, which is acquired only by a multitude of experiments; the power of speech, secured by a slow process of repeated acts of imitation; and the power of writing, gained in the same way. Success in every pursuit of life is attained by oft-repeated attempts, which finally induce a habit. As examples of the formation of _intellectual_ habits may be mentioned the facility gained in acquiring knowledge by means of repeated efforts, and the accuracy and speed with which the process of reasoning is performed after long practice in this art. As examples of _moral_ habits may be mentioned those which are formed by the oft-repeated exercise of self-government, justice, veracity, obedience, and industry. The will, as has been shown, gains a facility in controlling specific volitions and in yielding obedience to the laws of right action by constant use, as much as all the other mental powers.