The ancients, indeed, did not ask why nature submits to laws, but why it is ordered according to genera. The idea of genus corresponds more especially to an objective reality in the domain of life, where it expresses an unquestionable fact, heredity. Indeed, there can only be genera where there are individual objects; now, while the organized being is cut out from the general mass of matter by his very organization, that is to say naturally, it is our perception which cuts inert matter into distinct bodies. It is guided in this by the interests of action, by the nascent reactions that our body indicates--that is, as we have shown elsewhere,[85] by the potential genera that are trying to gain existence. In this, then, genera and individuals determine one another by a semi-artificial operation entirely relative to our future action on things. Nevertheless the ancients did not hesitate to put all genera in the same rank, to attribute the same absolute existence to all of them. Reality thus being a system of genera, it is to the generality of the genera (that is, in effect, to the generality expressive of the vital order) that the generality of laws itself had to be brought. It is interesting, in this respect, to compare the Aristotelian theory of the fall of bodies with the explanation furnished by Galileo. Aristotle is concerned solely with the concepts "high" and "low," "own proper place" as distinguished from "place occupied," "natural movement" and "forced movement;"[86] the physical law in virtue of which the stone falls expresses for him that the stone regains the "natural place" of all stones, to wit, the earth. The stone, in his view, is not quite stone so long as it is not in its normal place; in falling back into this place it aims at completing itself, like a living being that grows, thus realizing fully the essence of the genus stone.[87] If this conception of the physical law were exact, the law would no longer be a mere relation established by the mind; the subdivision of matter into bodies would no longer be relative to our faculty of perceiving; all bodies would have the same individuality as living bodies, and the laws of the physical universe would express relations of real kinship between real genera. We know what kind of physics grew out of this, and how, for having believed in a science unique and final, embracing the totality of the real and at one with the absolute, the ancients were confined, in fact, to a more or less clumsy interpretation of the physical in terms of the vital.