Not all modern scholastics, however, are willing thus to identify nature with substance. We have no intuitive insight into what any real essence or substance is; our knowledge of it is discursive, derived by inference from the phenomena, the operations, the conduct of things, in accordance with the principle, _Operari sequitur esse_. Moreover, the actually existing, concrete individual—a man, for instance—has a great variety of activities, spiritual, sentient, vegetative, and inorganic; he has, moreover, in the constitution of his body a variety of distinct organs and members; he assimilates into his body a variety of inorganic substances; the tissues of his body _appear_ to be different _in kind_; the vital functions which subserve nutrition, growth and reproduction are at least analogous to mechanical, physical and chemical changes, if indeed they are not really and simply such; it may be, therefore, that the _ultimate material_ constituents of his body remain _substantially unaltered_ in their passage into, and through, and out of the cycle of his vegetative life; that they retain their elemental _substantial forms_ while they assume a _new nature_ by becoming parts of the one organic whole, whose higher directive principle dominates and co-ordinates all their various energies.(283) If this be so there is in the same individual a multiplicity of really and actually distinct substances; each of these, moreover, has its own existence proportionate to its essence, since the existence of a created reality is not really distinct from its essence; nor is there any reason for saying that any of these substances is incomplete; what we have a right to say is that no one of them separately is a complete _nature_, that each being an _incomplete nature_ unites with all the others to form one _complete nature_: inasmuch as no one of them separately is an adequate intrinsic principle of all the functions which it can discharge, and is naturally destined to discharge, by its natural union with the others, whereas there results from their union a _new fundamental principle_ of a co-ordinated and harmonized system of operations—in a word, a _new nature_.