But we said further, that the laws to which such beings _were_ subject were of a peculiar nature, and it is particularly important to point out one respect in which these laws differ from the mechanical. Such laws as we find controlling the behavior of organisms, for example, are of the kind that may be called _laws of purpose_. We explain, that is to say, the conduct of organisms in terms of the end or purpose for the sake of which that conduct has taken place. This holds from the lowest biological functioning to the highest form of deliberate human behavior. If we consider the explanation which our author offers of the conduct of his unhappy hero, we see that in the end he has been exclusively interested in pointing out the motives to which the young man reacted. To point out motives is simply to recognize the end for the sake of which the act is accomplished. Now, although this type of explanation is in daily use among all men of all times, it was not erected into a scientific system before the reflections of Plato and Aristotle had shown of what extension it was susceptible. Aristotle in particular is responsible for having pushed to the very limit the notion that the greater part of nature’s happenings can be explained in terms of the end for the sake of which they occur. The whole drama of nature was to him what that of organic life is to most of us, the struggle of individual beings to accomplish their natural purposes. But, interested as Aristotle was in pushing this concept of purpose in nature to the limit, he could not blind himself to the fact that no purpose could be found in nature which was always and invariably accomplished or attained by the beings whose nature it was to struggle for it. Consequently, he was in the habit of saying that “laws of nature (by which he meant of laws of purpose) were descriptions of what happens always, or for the most part.” That is to say, they pointed out the behavior that was normal, but not free from exception. Nature was full of the accidental, of the abortive; and although later science did its best to exclude this notion of the accidental in nature’s happenings, the effort was uniformly unsuccessful and, I think, wrongly inspired. For it is exactly to the circumstance that laws of purpose are statements of average and not of unexceptional fact, that they owe their scientific value as labor-saving devices. And what is perhaps of more interest in the present connection, it is to this very lack of rigor in the laws governing animal and human behavior that we owe our right to regard the individual to which they apply as free.