Abstract
A new book by Stephen Engstrom repeats a criticism of Bruce Aune's of Kant's derivation of the universalizability formula of the categorical imperative. The criticism is that Kant omitted at least one substantive premise in the derivation of the formula: ‘Act only on that maxim through which you can at the same time will that it become a universal law.’ The grounds for the formula that are given in the Groundwork of the Metaphysics of Morals, however, are said to support only a weaker requirement, namely, that a maxim conform to a universal law. Hence, Kant omits at least one necessary substantive premise of the derivation. This paper attempts to show that nothing substantive is omitted from the argument. It only needs two principles of inference that it is assumed add nothing substantive to the premises.