Locke rejected what is essentially Kant's categorical imperative: “that one should do only as he would be done unto” (Essay 1, Kindle Locations 650-652). The rejection was based on the fact that the moral tenet does not demand the consent of reason, after all it is not unreasonable to question why we should obey the imperative.

From within Kant's theory of understanding as providing all objects and all relations between objects via apperception, and his theory of reason as supervening upon the stream of consciousness appercieved Locke's claim is justified. Only when Kant steps into the transcendental and argues for the reasonableness of morality based upon its occurrence in the noumenal realm does morality regain its demand upon the consent of reason; it is the noumenal objects that are involved in the initial meeting and they determine the will in the noumenal realm, which noumenal realm being nothing but logical possibilities syllogistically deduced from the absolute Idea or transcendental major premise means the initial determination of the will is determined by reason.

But this argument only goes to justify why there is morality in the world irrespective of the fact that it appears unreasonable for it to be there. It does not justify why Kant would identify the noumenal process determining the will (which determination will always be moral) with the categorical imperative as our phenomenal "guess" at what that noumenal process is. I know of no argument Kant makes to this identification. Does someone know of a passage?

2 Answers 2


Kant makes no such argument by which I mean Kant does not identify the categorical imperative with a "phenomenal 'guess.'" For him, the Categorical Imperative is a conclusion of reason and the limitations in his Critique of Pure Reason apply to understanding.

To put it another way, on Kant's account, that the CI is written in a book is trivial. That the argument for the CI can be derived from reason is what is important. Thus, he does not address an objection that needing encounter the CI in writing makes the CI a contingent reality in the world.

To understand why, we can look in several places. First, the Third Antinomy in the CPR. Here, the point is that the problems with the understanding cannot remove the space for morality, because morality is not accessed through the understanding. Kant develops this more positively across Groundwork, CPrR, Metaphysics of Morals, and Religion within the Bounds of Reason Alone.

In each of these texts, Kant presents somewhat different arguments for the Categorical Imperative as the rational morality that follows from human beings having both reason and a free will and being both rational choosers and empirically observable objects. To give a very rough sketch, what is common is always that we can only observe the phenomenal level of individuals and never gain access to their reason based on what happens. As material beings, they are subject to the very laws of physics that make morality seem impossible. But as rational beings, they are never mere subjects when it comes to moral action.


First, I did not say Kant identified the CI with a phenomenal guess. I said that every instance where we must take a moral position forces us to make a phenomenal guess because our reason is limited to the phenomenal realm. Moral reason imposes a conclusion upon us of which conclusion we cannot see the major or minor premise; God or noumena alone sees this and presents us with the conclusion fait accompli.

The tie between the CI and its justification in the noumenal realm is the nature of syllogism itself. A deductive syllogism is only valid when the conclusion drawn is already contained within the major premise of the syllogism. The CI ensures that the action can play the part of a major premise. Given an action that conforms to the CI one can randomly take any particular individual and conclude that the action is acceptable for them. In the same way one can deduce from the major premise that "all humans are mortal" that it is acceptable for any particular human.

  • First off, you should probably post this as a comment to the answer @virmaior gave. I'd also like to add to his excellent answer that reason is not limited to the phenomenal realm in Kant's thought. Speculative reason, dealing with questions of physics and metaphysics (such as the finitude or infinitude of the universe or the existence of God) can never be backed by intuition, but practical reason is not so limited. The moral law within us is itself evidence in Kant's view that we have access to the noumenal in the practical realm. Commented Jan 9, 2015 at 21:44
  • Laws can never be derived from experience or learned empirically, because of their universal scope and their necessity. Universality and necessity are predicates that can never be derived form experience, and so can only result from pure reason's access to the noumenal realm. Thus, we do have access, according to Kant, to the major premise you are describing. Commented Jan 9, 2015 at 21:47

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