It is easy to see why the question of free will brings into conflict these two rival systems of nature, mechanism and dynamism. Dynamism starts from the idea of voluntary activity, given by consciousness, and comes to represent inertia by gradually emptying this idea: it has thus no difficulty in conceiving free force on the one hand and matter governed by laws on the other. Mechanism follows the opposite course. It assumes that the materials which it synthesizes are governed by necessary laws, and although it reaches richer and richer combinations, which are more and more difficult to foresee, and to all appearance more and more contingent, yet it never gets out of the narrow circle of necessity within which it at first shut itself up.
A thorough examination of these two conceptions of nature will show that they involve two very different hypotheses as to the relations between laws and the facts which they govern. As he looks higher and higher, the believer in dynamism thinks that he perceives facts which more and more elude the grasp of laws: he thus sets up the fact as the absolute reality, and the law as the more or less symbolical expression of this reality. Mechanism, on the contrary, discovers within the particular fact a certain number of laws of which the fact is thus made to be the meeting point, and nothing else: on this hypothesis it is the law which becomes the genuine reality. Now, if it is asked why the one party assigns a higher reality to the fact and the other to the law, it will be found that mechanism and dynamism take the word simplicity in two very different senses. For the first, any principle is simple of which the effects can be foreseen and even calculated: thus, by the very definition, the notion of inertia becomes simpler than that of freedom, the homogeneous simpler than the heterogeneous, the abstract simpler than the concrete.