The complex classification of duties and of the moral statuses of acts in chapter 4 shows that the Categorical Imperative must have great powers of discrimination if it is really to provide a method for solving all those ethical problems for which Kant thinks it is appropriate. To most recent commentators, and to many earlier ones, it has seemed quite clear that the Categorical Imperative cannot be used to solve ethical problems. Mill wrote of Kant:

And a recent commentator, T. C. Williams, remarks:

It is certainly true that views both grotesque and bizarre have been attributed to Kant in the course of various discussions of the application of the Categorical Imperative. To use the Formula of Universal Law as a test of the moral status of acts is often held to commit one to rigourism – to the view that all moral principles must be very general. Sometimes it is thought to involve the claim that all acts must be either obligatory or forbidden, and that there is no other moral status or that principles of action can be logically deduced from a purely formal principle, or that moral principles must abstract from ends, and even that any act which is enjoyed must be immoral. The inadequacies of these attributions have been well documented, particularly by Ebbinghaus and Paton, and more recently by Singer and Williams. It would, therefore, not be fruitful to go over past commentaries to see whether each is just or not in its attribution of grotesque and bizarre viewpoints.