How is it then that certain external things are said to be natural, and other contrary to Nature?

Why, just as it might be said if we stood alone and apart from others. A foot, for instance, I will allow it is natural should be clean. But if you take it as a foot, and as a thing which does not stand by itself, it will beseem it (if need be) to walk in the mud, to tread on thorns, and sometimes even to be cut off, for the benefit of the whole body; else it is no longer a foot. In some such way we should conceive of ourselves also. What art thou?—A man.—Looked at as standing by thyself and separate, it is natural for thee in health and wealth long to live. But looked at as a Man, and only as a part of a Whole, it is for that Whole's sake that thou shouldest at one time fall sick, at another brave the perils of the sea, again, know the meaning of want and perhaps die an early death. Why then repine? Knowest thou not that as the foot is no more a foot if detached from the body, so thou in like case art no longer a Man? For what is a Man? A part of a City:—first of the City of Gods and Men; next, of that which ranks nearest it, a miniature of the universal City. . . . In such a body, in such a world enveloping us, among lives like these, such things must happen to one or another. Thy part, then, being here, is to speak of these things as is meet, and to order them as befits the matter.