See the Grundlegung zur Metaphysik der Sitten (pp. 269---273, Hartenstein; Abbott's translation [1879] pp. 54--61). Here Kant first says, ``There is therefore but one categorical imperative, namely, this: Act only on that maxim whereby thou canst at the same time will that it should become a universal law. Now, if all imperatives of duty can be deduced from this one imperative as from their principle … we shall at least be able to show what we understand by [duty] and what this notion means.'' He then demonstrates the application of the principle to four cases, selected as representative of ``the many actual duties''; and continues: ``if now we attend to ourselves on occasion of any transgression of duty, we shall find that we in fact do not will that our maxim should be a universal law, for that is impossible for us''…: then, summing up the conclusion of this part of his argument, he says, ``we have exhibited clearly and definitely for every practical application the content of the categorical imperative which must contain the principle of all duty, if there is such a thing at all''.