To explain a power, on the other hand, is (the power itself being assumed, though not comprehended, _ut qui datur, non intelligitur_) to unfold or spread it out: _ex implicito planum facere_. In the present instance, such an explanation would consist in the reduction of the idea of Life to its simplest and most comprehensive form or mode of action; that is, to some characteristic _instinct_ or _tendency_, evident in all its manifestations, and involved in the idea itself. This assumed as existing in _kind_, it will be required to present an ascending series of corresponding phenomena as involved _in_, proceeding _from_, and so far therefore explained _by_, the supposition of its progressive intensity and of the gradual enlargement of its sphere, the necessity of which again must be contained in the idea of the tendency itself. In other words, the tendency having been given in _kind_, it is required to render the phenomena intelligible as its different degrees and modifications. Still more perfect will the explanation be, should the necessity of this progression and of these ascending gradations be contained in the assumed idea of life, as thus defined by the general form and common purport of all its various tendencies. This done, we have only to add the conditions common to all its phenomena, and, those appropriate to each place and rank, in the scale of ascent, and then proceed to determine the primary and constitutive forms, _i.e._ the elementary powers in which this tendency realizes itself under different degrees and conditions.(7)