Kant’s Groundwork aims to use what Kant calls “pure philosophy,” or intellect alone, to develop a moral philosophy. What is ethical has to be done for the sake of the law, and for that reason our experience can’t serve as a viable basis for a durable moral philosophy. By writing the Groundwork, Kant hopes to establish the possibility of moral philosophy, and to clarify its core concepts, before moving onto an elucidation of the philosophy itself.
Kant opens the Groundwork by attacking the theory of moral sentiments, which the Scottish Enlightenment philosophers like Adam Smith and David Hume had developed and which was very influential. Morality, Kant claims, can never be based on inclination or feeling, as Hume and Smith had argued. To act morally means to act in accordance with the moral law, and inclination and feeling do this only accidentally. Our feelings might steer us towards what is good; but the next moment, they might just easily steer towards what is bad. In any case, they do not give us a firm criterion for distinguishing the two. The only firm basis for making sure an action is in accordance with the moral law is to do it because it is in accordance with the law, regardless of how one feels about it.
From this principle, Kant is able to derive a principle for formulating moral actions: always act in such a way that your action could be the basis for a universal law. Kant calls this the categorical imperative. Only the categorical imperative conceives of actions as universally necessary from the form of their judgment alone; all other bases for deciding moral action are necessarily influenced by feelings of pleasure or displeasure, and therefore situational, and not truly moral. The categorical imperative also insists that we treat others as “ends” in themselves. It forbids us from using other human beings as a “means” to this or that goal, since only the dignity of humanity is a truly universally acknowledged end.
Insofar as we use reason, we are both lawgivers and subjects of the law. When we use the categorical imperative to formulate moral judgments, we imagine ourselves as belonging to a community in which each person is both lawmaker and subject. Kant calls this the kingdom of ends.
Kant closes the Groundwork by admitting that, while the categorical imperative is the only legitimate formulation for moral action, he cannot prove that we must be moral. Human beings live in two worlds: the world of the mind and the world of appearances. To be free, and therefore moral, an action has to be self-caused. That is why moral action is moral: because of the form in which we think it. But to take effect in the world, it has to join the chain of infinite causation that constitutes nature. Therefore, it would no longer be free. The moral law is, therefore, something fundamentally incomprehensible to us, that we must nonetheless admire.
