Kant deepens this argument in characteristic fashion by steering it into the domain of morality. We are moral beings. We have moral concepts like “right” and “wrong” and “good” and “evil.” We “ought” to do this and “ought not” to do that. Try as we can, we cannot avoid this way of thinking and acting. Morality is an empirical fact no less real than anyother experience in the world. Kant argues that for these concepts to have any meaning or applicability whatsoever, it must be the case that we have a choice whether to do something. Ought implies can. This is not to deny that factors both material and unconscious might influence our decision. But even so, we are at least sometimes at liberty to say yes to this option and no to that option. If we never have such a choice, then it is simply false to say I “should” do this and “shouldn’t” do that because there is no possibility of deciding one way or the other. For anyone to recommend one course or action instead of another is completely pointless. If determinism is true, then no one in the world can ever refrain from anything that he or she does. The whole of morality—not just this morality or that morality but morality itself—becomes an illusion.

Our whole vocabulary of praise and blame, admiration and contempt, approval and disapproval would have to be eradicated. If someone murdered his neighbor, or exterminated an entire population, we would have no warrant to punish or even criticize that person because, after all, he was simply acting in the manner of a computer program malfunctioning or a stone involuntarily rolling down a hill.

But Kant says that this way of thinking is not only unacceptable, but is also impossible for human beings. People who operate outside the sphere of morality we call psychopaths, and rather than assign them to teach philosophy we put them in straightjackets. We are, by our nature, moral. And it follows from this that we are free, at least to a certain degree, to choose between alternative courses of action because this is the only way we can think and act morally.

Kant follows this train of reasoning to its remarkable conclusion: we enjoy at least some measure of freedom in the operation of our will. This freedom means doing what we want to do or what we ought to do, as opposed to what we have to do. Freedom implies autonomy, which Kant distinguishes from subservience to natural inclination. So at least some of what we think and do is not governed by the necessity imposed by the laws of science. If I give a dollar to a man on the street, the movements of our bodies are determined by nature, but my choice to give and his choice to take are free decisions that we both make.

It follows that there is an aspect of our humanity that belongs to the world of science, and there is an aspect of our humanity that is outside the reach of scientific laws. Simultaneously, we inhabit the realm of the phenomenal, which is the material realm, and also the realm of the noumenal, which is the realm of freedom. It is the noumenal realm, the realm outside space and time, that makes possible free choices, which are implemented within the realm of space and time. Materialism tries to understand us in two dimensions, whereas in reality we inhabit three.