Kant starts off making two distinctions regarding kinds of knowledge, empirical/rational and formal/material. Empirical or experience-based knowledge is compared with rational knowledge, which is independent of experience. This distinction between empirical and rational knowledge rests on a difference in sources of evidence used to support the two different kinds of knowledge. Formal is compared with material knowledge. Formal knowledge has no specific subject matter; it is about the general format of thinking about any subject matter whatsoever. Material knowledge is of a specific subject matter, either nature or freedom. Rational knowledge is metaphysics, of which there are two branches, the metaphysics of nature and of morals.
The metaphysics of nature is supposed to provide rational knowledge of the laws of nature. These are not empirical laws; they are more like universal principles of nature that any empirical physical would presuppose, such as that no event in nature occurs without a natural cause. The metaphysics of freedom is supposed to provide knowledge of the laws of freedom. These are the universal rules, which free agents form to govern them. Therefore, Kant’s grounding, his initial attempt at a critique of rational reason, is an investigation of the possibility of purely rational knowledge of morals. Take, for example, the Moral Rule: Thou shall not lie. If the moral law is valid as the basis of moral obligation or duty, then it must be necessary. Kant using the word “necessity” means that the rule obligates or binds whatever the conditions or in all circumstances. It also means that the rule applies to all rational beings and not only to human beings.
In this second sense we can say that the rule is universally binding. So in fact, moral rules are universal and necessary. If a moral rule is to be universal and necessary, the moral law must be derived from concepts of pure reason alone. Therefore, if a moral rule or law can only be derived from reason alone, there must be a pure moral philosophy whose task is to provide such a derivation.
According to Kant good will and only a good will is intrinsically good. Kant distinguishes two different types of intrinsic or extrinsic goods. If a thing is only extrinsically good, then it is possible for that thing not to be good, or to be bad or evil. Intrinsic goodness is goodness in itself; if a thing is intrinsically good, its goodness is essential to it; and its goodness is not a function of factors other than itself. Kant holds that only a good will, not happiness, is intrinsically good. The idea that it is reason rather than natural impulse that guides action for the sake of happiness is false. Parts of a person perform their functions by surviving and this provides happiness for the person. Reason functions poorly in serving that purpose; instinct does better job. Natural instinct rather than reason provides better for happiness.
Kant distinguishes between having a reason to act and acting for a reason. The motivating reason is the reason for which agent acts. A justifying reason is the reason that justifies, warrants, and provides the criterion of rightness for the action. The agent’s motivating reason might or might not provide a justifying reason for his action. Kant then defines three types of motivating reasons. One type of non-moral motivation is natural motivation. Action in accord with duty is motivated by immediate or direct inclination. Direct inclination includes such motives as love, sympathy, instinct for self-preservation, or the desire for happiness. The other type of non-moral motivation is prudence. An action in agreement with duty, but motivated by prudence, is action motivated by the pursuit of self-interest or happiness. Since all human beings naturally desire happiness, prudential motivation is indirectly motivated by a natural motivation.
Moral motivation is the third type of motivation. The action is not only in agreement with duty, but motivated by duty, done from duty, or for sake of duty. The agent’s motivating reason, the reason for which he acts, is that the action is what morality demands and he wants above all to do what reason demands.