were exactly known, his conduct could be calculated as certainly and as precisely as an eclipse of the moon (ibidem, p. 177; R., p. 230): he nevertheless makes an assumption of freedom (although only idealiter, and as a postulate) by his celebrated conclusion: “You can, because you ought”; and this on the strength of his precious ethical basis, which, as we see, floats in the air incorporeal. But if it has once been clearly recognised that a thing is not, and cannot be, what is the use of all the postulates in the world? It would be much more to the purpose to cast away that on which the postulate is based, because it is an impossible supposition; and this course would be justified by the rule a non posse ad non esse valet consequentia; and by a reductio ad absurdum, which would at the same time be fatal to the Categorical Imperative.