Discourses, "How Magnanimity is Consistent with Care" (§2)

“How then is it said that some external things are according to nature and others contrary to nature? It is said as it might be said if we were separated from union (or society): for to the foot I shall say that it is according to nature for it to be clean; but if you take it as a foot and as a thing not detached (independent), it will befit it both to step into the mud and tread on thorns, and sometimes to be cut off for the good of the whole body; otherwise it is no longer a foot.”