Practical Reason and the Summum Bonum

In the wake of the Critique of Pure Reason, where Kant slams the door on metaphysical knowledge of the objects of the noumenal realm, we find the Critique of Practical Reason. In this work Kant focuses almost solely on the philosophy of morality and its insight concerning knowledge of the noumenal realm. For Kant, the moral law does not consist in subjective feelings of what one should do because the moment the feeling changes so would the ought, but rather moral law consists solely in an objective universal, specifically its form alone, that one should always do, even in spite of consequences and/or subjective feelings. This is known more succinctly as the Categorical Imperative. For Kant the Categorical Imperative is a priori in nature, not stemming from the a posteriori phenomenal realm, as ethical theories based upon ideas such as utility do, but from that of the noumenal. This is an important concept in the Critique because if the moral law finds its source in the phenomenal then it leaves the human will not free but rather determined by prior causes therefore removing the “oughtness” of the Categorical Imperative for ought implies can, as Kant states, “Freedom and an unconditioned practical law reciprocally imply each other” (29). For Kant the fundamental starting point of the Categorical Imperative is to “act so that the maxim of your will can always at the same time hold good as a principle of universal legislation” and this is in fact, as mentioned earlier, synthetic a priori based upon pure reason (31-32).

Now a question must be asked, namely, how is it shown that this Categorical Imperative can actually make it necessary that pure reason be practical? It seems that for Kant, the use of pure theoretical reason, while establishing the necessity of the noumenal, left us with absolutely no knowledge of the things contained therein, hence the infamous phenomenal/noumenal split. So, where then the Categorical Imperative? As noted, it is a priori in form, not coming from the world of sense experience, yet it seems clear enough that we certainly have knowledge of it. For Kant the moral law gives us an absolute fact, “which points to a pure world of understanding” (44). Therefore, it seems that, in light of the fact of the Categorical Imperative, we have true knowledge of something that is not based upon the phenomenal world of sense but rather upon the noumenal world which can only be accessible through reason, pure practical reason. Therefore, in the face of the moral law, practical reason seems to be necessary, for apart from it we could not have knowledge of the moral law, of which we clearly have knowledge. It is vitally important to stress the fact that this knowledge cannot come from pure theoretical reason, which is based upon the sensing of the phenomenal world, for if it were it would be a posteriori in nature which, as Kant demonstrated in the Critique of Pure Reason, cannot give rise to knowledge of anything in the noumenal realm, hence the necessity of practical reason. This seems like a reasonable conclusion for Kant to make seeing that in Pure Reason he shut the door to metaphysical knowledge of the noumenal by means of scientific inquiry. Seeing the paradox of knowledge of something not based upon phenomena, practical reason is “necessarily needed.”

From this we can rightfully inquire into Kant’s use of the summum bonum or the highest good. It seems as though this too is a necessary outworking of his use of the Categorical Imperative. It would seem that Kant’s argument is that the summum bonum is the ultimate goal of the moral law. He defines the summum bonum as the highest state of virtue coupled with the highest state of happiness. It is important to note that he seems to place the existence of happiness with the presence of virtue and not the other way around. Once again, as in the case of the Categorical Imperative, the summum bonum is an a priori idea that is gained before experience of the sensible world, (lending itself as evidence for virtue being the cause of happiness) which humans seem to have as the ultimate goal of the there morality by means of the Categorical Imperative. The Categorical Imperative seems almost useless without the existence of the summum bonum because what would the CI be tending towards if it weren’t for the sb? From this idea Kant also postulates the existence of an immortal self that is separate from the sensible phenomenal realm, and therefore part of the noumenal realm. This must be the case, reasons, Kant because the summum bonum cannot be reached here in our lives, so there must be more, an afterlife, so to speak. He also postulates God, saying that the possibility of the summum bonum obtaining is directly linked to the existence of God, the only one capable of rewarding the highest virtue, therefore producing the greatest happiness. This idea Kant links to the doctrine of the Kingdom of God within Christianity.