Bolzano’s main objection against the Categorical Imperative was that we cannot derive from it alone — as Kant supposed — whether a given act ought to be done or not. Kant’s instruction to ask ourselves of a maxim whether we can will without contradicting ourselves that it should become a universal law is of no use, according to Bolzano, since for him there is no practical proposition or ought proposition whose contradictory opposite is self-contradictory. This, however, is not a decisive argumen