Having thus made clear the coincidence of empirical concepts and the natural sciences, we must determine exactly the meaning of the word "natural," which is used as qualifying these sciences. It has not seemed advisable to change it, since its use is so deeply rooted, although we have, on the other hand, already given its synonym in qualifying these sciences as "empirical." What is _nature_? The first meaning of "nature" is the "opposite" of "spirit," and designates the natural or material moment in relation to the spiritual, the mechanical in relation to the teleological moment, the negative moment in relation to the positive. Thus, in the transition from one form of the spirit to another, the inferior form is like matter, ballast, or obstacle, and so is the negation of the superior form. Hence reality is imagined as the strife of two forces, the one spiritual and the other material or natural. It is superfluous to repeat that the two forces are not two, but one, and that if the negative moment were not, the positive moment could not be. The pigeon (says Kant), which rises to take flight, may believe that had it not to vanquish the resistance of the air, it would fly still better. But the fact is that without that resistance, it would fall to earth. In this sense, there is no science of Nature (of matter, passivity, negation, etc.) distinguishable from that of Spirit, which is the science of itself and of its opposite, and the science of itself only in so far as it is also the science of its opposite. [Sidenote: _Nature as practical activity._] But in another sense, _nature_ is, not indeed the opposite of spirit, but something distinct _in_ the spirit, and especially distinct from the cognitive spirit, as that form of spirituality and activity which is not cognitive. A non-theoretical activity, a spirituality which should not be in itself knowledge, cannot be anything but the _practical_ form of the spirit, the will. _Man makes himself nature_ at every moment, because at every moment he passes from knowing to willing and doing and from willing and doing returns to knowing, which is the basis for new will and action. In this sense, the science of nature, or the philosophy of nature, could not be anything but the philosophic science of the will, the Philosophy of the practical. [Sidenote: _Nature in the gnoseological sense, as naturalistic or empirical method._]