In a similar vein, the earliest conceptions of natural evolution attributed it to the coworking of two principles, that of Love or union and that of Hate or dissolution. The process is here distinguished from the material of nature, but is still described in the language of practical life. A distinction between two aspects of vital phenomena is the next step. These may be regarded in respect either of the motion and change which attend them, or the rationality which informs them. Life is both effective and significant. Although neither of these ideas ever wholly ceases to be animistic, they may nevertheless be applied quite independently of one another. The one reduces the primitive animistic world to the lower end of its scale, the other construes it in terms of a purposive utility commensurable with that of human action. Now it is with _mechanism_, the former of these diverging ways, that the development of materialism is identified. For this philosophy a thing need have no value to justify its existence, nor any acting intelligence to which it may owe its origin. Its bulk and position are sufficient for its being, and the operation of forces capable of integrating, dividing, or moving it is sufficient for its derivation and history. In short, there is no rhyme or reason at the heart of things, but only actual matter distributed by sheer force. With this elimination of the element of purposiveness from the hylozoistic world, the content and process of nature are fitted to one another. Matter is that which is moved by force, and force is the determining principle of the motions of matter. Materialism is now definitely equipped with its fundamental conceptions. [Sidenote: Materialism and Physical Science.] § 105. The central conceptions of materialism as a philosophical theory differ from those employed in the physical sciences only in what is demanded of them. The scientist reports upon physical phenomena without accepting any further responsibility, while those who like Lucretius maintain a physical metaphysics, must, like him, prove that "the minute bodies of matter from everlasting continually uphold the sum of things." But, though they employ them in their own way, materialists and all other exponents of naturalism derive their central conceptions from the physical sciences, and so reflect the historical development through which these sciences have passed. To certain historical phases of physical science, in so far as these bear directly upon the meaning of naturalism, we now turn. [Sidenote: The Development of the Conceptions of Physical Science. Space and Matter.]