By insisting on the fact that the moral imperative is not concerned with what might or might not be done, Kant discovered the essential dimension of ethics: the dimension of desire , which circles around the real qua impossible. This dimension was excluded from the purview of traditional ethics, and could therefore appear to it only as an excess.
So Kant’s crucial first step involves taking the very thing excluded from the traditional field of ethics, and turning it into the only legitimate territory for ethics. If critics often criticize Kant for demanding the impossible, Lacan attributes an incontestable theoretical value to this Kantian demand. 3