And this great example of the laws of motion shows with the utmost clarity how much difference there is between these three cases, to wit, firstly an absolute necessity metaphysical or geometrical, which may be called blind, and which does not depend upon any but efficient causes; in the second place, a moral necessity which comes from the free choice of wisdom in relation to final causes; and finally in the third place, something absolutely arbitrary depending upon an indifference of equipoise, which is imagined, but which cannot exist, where there is no sufficient reason either in the efficient or in the final cause.