In the First Section of the Groundwork of the Metaphysics of Morals, Kant argues that a good-willed person “under subjective limitations and hindrances” (G 397) is required “never to act except in such a way that [she] could also will that [her] maxim should become a universal law” (G 402).2 This requirement has come to be known as the Formula of Universal Law (FUL) version of the Categorical Imperative, an “ought” statement expressing a command of reason that “represent[s] an action (...) as objectively necessary of itself, without reference to another end” (G 414). The question of how to understand and apply the FUL has received a great deal of attention in recent years. But Kant’s reasoning for the claim that a good-willed person (of a certain kind) acts in accordance with the FUL has not been investigated with the same degree of thoroughness. My purpose in this paper is to render the structure of Kant’s argument perspicuous, and thereby contribute to its proper evaluation by identifying its true strengths and weaknesses.3 Let us call Kant’s argument “K” and its conclusion “C”. The task at hand requires identification of K’s premises and of the reasoning by means of which C is derived. One of the advantages of clarifying K’s structure in this way is that doing so permits us to answer questions that continue to puzzle even the most sympathetic readers of the First Section. Some of these questions concern three “Propositions” to which Kant 1 draws our attention in the course of his presentation. The First Proposition (call it “P1”) is left unstated, but most commentators agree that it (or at least part of it) should be rendered as follows: (P1) A human action has moral worth only if it is done from duty.4 Kant states the other two propositions (call the Second “P2” and Third “P3”) explicitly: (P2) An action from duty has its moral worth not in the purpose to be attained by it but in the maxim in accordance with which it is decided upon. (G 399). (shrink)

This paper introduces a referential reading of Kant’s practical project, according to which maxims are made morally permissible by their correspondence to objects, though not the ontic objects of Kant’s theoretical project but deontic objects (what ought to be). It illustrates this model by showing how the content of the Formula of Universal Law might be determined by what our capacity of practical reason can stand in a referential relation to, rather than by facts about what kind of beings we (...) are (viz., uncaused causes). This solves the neglected puzzle of why there are passages in Kant’s works suggesting robust analogies between mathematics and ethics, since to universalize a maxim is to test a priori whether a practical object with that particular content can be constructed. An apparent problem with this hypothesis is that the medium of practical sensibility (feeling) does not play a role analogous to the medium of theoretical sensibility (intuition). In response I distinguish two separate Kantian accounts of mathematical apriority. The thesis that maxim universalization is a species of construction, and thus a priori, turns out to be consistent with the account of apriority that informs Kant’s understanding of actual mathematical practice. (shrink)