A person is obligated or ought to do a thing when he has the intellect to perceive what is _best_, and thus _right_, and the moral susceptibilities just described. When he is destitute either of the intellect or of these susceptibilities, he ceases to be a moral and accountable being. He can no longer be made to feel any moral obligations. CHAPTER XV. THE NATURE OF MIND.—THE WILL. The power _to choose_ exists in other animals as well as in man, so that it is not this faculty which distinguishes our race from the brutes. It is another part of our nature which elevates us above the lower animals, which will now be described. Irrational Free Agency. We have seen that desires for good are measured as to their strength or feebleness by our own consciousness, and that in multitudes of cases we choose those things which excite _the strongest_ desire. A mind so constituted as never to be able to choose any thing but that which excites the strongest desire, would be entirely dependent on circumstances, and thus the helpless sport of chance. This is the kind of free agency which belongs to the brutes, and may properly be called _irrational free agency_. Rational Free Agency. In contrast with the above, we have already described the mind of man as possessing the power to choose _either_ that which excites the strongest desire or that which the intellect decides to be _best for all concerned_. When there is nothing to excite desires, there is no power at all to choose; so that motives are as indispensable to the action of the will as physical causes are to the movement of matter. The more strongly desire is excited the more the power of choice is increased. This gives rise to the universal use of language which characterizes motives as stronger or weaker according as desire is more or less powerful. The greater part of our choices are for things which are _best_, so that there is no conflict between what excites the strongest desire and what is best for all. Thus to eat, drink, walk, sleep and perform most of the daily duties of life, are cases where the strongest desire and what is best coincide. In all such cases we choose that which excites the strongest desire. And when we assign the cause or reason for our choice, we say it was the strongest desire which was the _cause_; that is to say, it was the _occasional_ cause of our choice. But our own mind is the only _producing_ cause of its own volitions. This exhibits the grand principle of _free agency_ in distinction from its opposite, which is called _fatalism_, viz.: _Motives are producing causes of desire, and are occasional causes of choice. Mind itself is the only producing cause of choice, having power to choose either that which excites the strongest desire or that which reason and conscience decide to be best for all concerned._