De Rervm Natvra Constantivm Scientia, Principiis Et Affectionibvs Commvnibvs, Dispvtatio

And so much for the first chapter. Now let us turn our speech to natural things themselves and their proper affections, although to understand these things, it brings no small momentum to understand how a thing moves from itself or by nature. Next, we shall treat of nature.

CHAPTER II.

ON NATURE.

XVII. NATURE is defined as a principle and cause of motion and rest in that in which it exists primarily and of itself, and not according to accident. Each word needs explanation: First, "cause" is not said in the proper sense, as if motion and rest followed nature as effects distinct in reality in a universal way; for many feel that local motion does not differ in reality from the mobile thing. The same must be thought concerning rest, if the name is used for the objective meaning. For rest is nothing other than permanence in a natural thing with the same limit. But if it is taken for the formal meaning, it is indeed distinguished from nature by reality; for it is a negation by which we deny in our mind that the natural thing is moved any further, but nature is by no means the cause of that negation. Wherefore, it is called a cause in that sense, by which, because of an innate power, according to a law prescribed by GOD, rest or motion—that is, the permanent or successive conjunction of a limit—is due to it.

XIIX. And with this interpretation employed, it can nevertheless be called a cause, either because it is actually a principle so that a thing may move or rest, or because it is a principle of motion and rest in near potentiality. Whichever way you take it, the definition is perfect, though in the first way it is only accidental, and in the latter it is essential. For it happens to nature, as long as it retains the name of nature, that it actually moves or actually rests. Sometimes, however, it neither rests nor moves, when, to be sure, it is driven by force against its innate inclination or is retarded from its natural course.