Kant imagines that all those participating in and adhering to his system of morality all belong to a union known as the Kingdom of Ends, in which all rational beings are united under common laws, that is, the Categorical Imperative, as well as any other laws that pass the CI’s filtering system. These laws have universal validity and can be applied to any rational beings. This is a cosmopolitan type of morality. He writes that we must abstract away any personal differences that arise between rational beings, as these difference, e.g., gender, race, religion, culture, or language, have no impact on morality, whatsoever.

This position is meant to directly repudiate Hume’s emotivism and cultural subjectivism. While Hume thinks that inclinations and hence morals differ from culture to culture according to what is acceptable behavior, Kant roots his morality in an objective standard—a standard as objective as mathematics. That standard is dignity, which is based on rational autonomy. Here, Kant introduces the ought/can distinction in differentiating between subject and object. In order to have a duty to do something, one must be able to do it in the first place. I cannot, for instance, have an absolute duty to cure wold hunger and poverty, since it is utterly impossible for me to achieve this. I cannot therefore be faulted when I do not complete this duty, since I was, and am completely unable, to do it. But I am able to fulfill some duties—most dues, in fact, even though I am not perfect. Take the duty ‘Do unto others as you have them do unto you’. I have a duty to fulfill this principle because I am perfectly capable of carrying it out.

A rock, on the other hand, is in principle not capable of carrying out any duties at all, since it has no will, is not autonomous, and has no rationality. This is why dignity cannot belong to the rock (the object), but can belong to me (the subject). Of course, in having this dignity, I have to take great care in avoiding external influence and circumstances from having an impact on my actions. I must be internally free to will this way or that, and this freedom needs to be cultivated, as it certainly is not easy to ignore circumstances or external reasons for acting in a certain way that takes away from duty. In fact, Kant prides himself on his ability to completely ignore external circumstances, so that he can be free to rationally follow his moral duties, with no mind to distractions that attempt to dissuade. 

Regarding external factors, Kant vehemently disagrees with Aristotle. External goods, for instance, are far too contingent and arbitrary to be considered as part of the moral equation. Since duty is involved and duty requires ought/can, it must be the case that everyone is able to achieve conformity to the moral laws. Once we understand Kant’s insistence on duty, we realize that his rejection of external goods is not for trifling reasons or aesthetic considerations. In order for duty to be absolute, it must be achievable by all rational beings. We cannot exclude women or slaves from the equation simply because they cannot achieve Aristotle’s eudemonia. Yet, there are a few points of agreement between the two. Kant thinks that nature is teleological, that it is purposive. He echoes the claim that ‘nature does nothing in vain’, although of course he cannot include flourishing in his account of morality, since it’s based on arbitrary external factors. Anyone must be able to enter the Kingdom of Ends, the place where everybody treats each other as ends in themselves, rather than merely as means to some other end.

This Kingdom, Kant acknowledges, is just an ideal. He knows that such a union will never exist, because the requirements of morality are too strict and difficult to achieve. Being part of the universal Kingdom of Ends, each rational member is a legislator. By reason alone, he can create new duties, provided they pass the test of the Categorical Imperative. The CI is a five-part test, with each part essentially saying the same things, albeit in slightly different ways. If the action in question passes the test, then it becomes a moral duty not just for this one rational being, but for all, regardless of their wealth, status, lineage, physical appearance, or geographical location.

This abstract reasoning is essential to Kant’s take on morality. He arrives on the scene with the goal of answering Hume’s skeptical conclusions, which ‘woke him from his dogmatic slumber’. Hume, as radical empiricist, divided knowledge into two categories: relations of ideas and the facts of experience. Relations of ideas are merely tautological concepts. The second term in the statement can be deduced from the first, and so nothing profound is being said. The statement is necessarily true, but trivially so. The facts of experience are uncertain and contingent apprehensions of the world through sense experience. There is no room here for the absolute, especially when inductive reasoning is being used.

This account clearly does not leave much room for morality, since Hume was eager to cast anything to the fire that did not fit in either of these categories as sophistry and illusion. As it was clear to Hume that any objective morality had no place, it must be emotive in nature, with no real duties to be spoken of.

Kant responds to this by creating a similar division, which he calls analytic and synthetic, both relating almost exactly to relations of ideas and the facts of experience. Working based on a mechanistic view of nature as provided by Newton, Kant recognized that mathematics—while conceived entirely by rationality—nevertheless held necessarily true in the empirical world. The same was the case for morality. He called this category: synthetic a priori, since ideas conceived purely in the mind actually held true (necessarily so) in the world of appearances. That is, no one would even begin to look for a counterexample to the Pythagorean theorem, even though it is purely abstract. This is also true about morality. It is something conceived of in the mind, yet it speaks to concrete actions. This is how Kant made room for the existence of morality that applied to all rational beings at all times.