The controversy had begun in the previous century and was rife through the entirety of the modern period. Following the implications of his mechanical description of physical substances, Descartes argued that force is reducible to the mathematical quantity of motion observable in matter. Descartes contended that this quantity is conserved in the universe. Nature is matter in motion, and motion is the explanatory principle. “Force” is the product of mass and velocity (mv), a quantity called “quantity of motion” or “dead pressure” then and momentum now.[11] Beyond this, for Descartes, “force” has no further meaning. Cartesian essence can be isolated to physical and mental substances and force is neither of these. Force is not a dynamic essence, nor an essence at all. It is merely a quantity of motion calculable in another substance.  By his rendering, Descartes reduced physics to kinematics.