Thus the _continuity or the alteration of the principles_ on which an idea has developed is a second mark of discrimination between a true development and a corruption. SECTION III. THIRD NOTE. POWER OF ASSIMILATION. In the physical world, whatever has life is characterized by growth, so that in no respect to grow is to cease to live. It grows by taking into its own substance external materials; and this absorption or assimilation is completed when the materials appropriated come to belong to it or enter into its unity. Two things cannot become one, except there be a power of assimilation in one or the other. Sometimes assimilation is effected only with an effort; it is possible to die of repletion, and there are animals who lie torpid for a time under the contest between the foreign substance and the assimilating power. And different food is proper for different recipients. This analogy may be taken to illustrate certain peculiarities in the growth or development in ideas, which were noticed in the first Chapter. It is otherwise with mathematical and other abstract creations, which, like the soul itself, are solitary and self-dependent; but doctrines and views which relate to man are not placed in a void, but in the crowded world, and make way for themselves by interpenetration, and develope by absorption. Facts and opinions, which have hitherto been regarded in other relations and grouped round other centres, henceforth are gradually attracted to a new influence and subjected to a new sovereign. They are modified, laid down afresh, thrust aside, as the case may be. A new element of order and composition has come among them; and its life is proved by this capacity of expansion, without disarrangement or dissolution. An eclectic, conservative, assimilating, healing, moulding process, a unitive power, is of the essence, and a third test, of a faithful development. 2. Thus, a power of development is a proof of life, not only in its essay, but especially in its success; for a mere formula either does not expand or is shattered in expanding. A living idea becomes many, yet remains one. The attempt at development shows the presence of a principle, and its success the presence of an idea. Principles stimulate thought, and an idea concentrates it.