Immanuel Kant developed his ideas of transcendental idealism into a comprehensive system of thought that included epistemology (the study of knowledge), metaphysics (the nature of reality), and ethics (moral philosophy). He saw his moral philosophy as a response to the Enlightenment philosophes, who had sought to apply logic and reason to all aspects of life. A central tenet of Kant’s moral philosophy was that as rational beings, we have innate concepts of what is good and evil, and the freedom to choose whether to act on our own behalf or not. But he disagreed with the philosophes’ view that morality could be derived solely from the consequences of acts. Instead, he believed that morality was based on intentions, not outcomes.
If there is a good reason why something is right or wrong—for example, because of its intrinsic value or because it promotes peace—then it must be universally valid, regardless of the consequences. He added the notion that it is wrong to treat others as merely a means to an end, and that morality is based on reason, like science. Moral laws, he wrote, cannot have any exceptions, since otherwise, they would be arbitrary. Kant famously stated this principle as “Act only according to maxima that you can will also to become a universal law”, later adding that it is always wrong “to treat others as mere means”. Universal moral laws might seem appealing, but they are just as hard to justify as pure consequentialism. For example, if it is wrong to tell lies, then is it morally wrong to lie to protect the fugitive slave we are sheltering?
