  The first of these arguments presses on the relationship between the  nature of matter and the laws of motion. Leibniz, in effect, argues  that the thesis that the whole essence of matter is extension saddles Cartesians with a dilemma: they must either hold that the laws of  motion are grounded in the nature of extension, or that God acts  directly to bring about the lawful regularities that are observed in  the world. Leibniz maintains that the first horn is inconsistent with the true laws of motion, while the second horn leads to the untenable postulation of perpetual miracles. In order to better appreciate  Leibniz’s line of reasoning here, it is worth unpacking a  little his thinking with respect to each horn of the dilemma. 