The Metaphysics of Morals by Immanuel Kant Chapter 2 Page 39

words empirically, whether there is such an imperative at all, but it is rather to be feared that all those which seem to be categorical may yet be at bottom hypothetical. For instance, when the precept is: “Thou shalt not promise deceitfully”; and it is assumed that the necessity of this is not a mere counsel to avoid some other evil, so that it should mean: “Thou shalt not make a lying promise, lest if it become known thou shouldst destroy thy credit,” but that an action of this kind must be regarded as evil in itself, so that the imperative of the prohibition is categorical; then we cannot show with certainty in any example that the will was determined merely by the law, without any other spring of action, although it may appear to be so.

For it is always possible that fear of disgrace, perhaps