Kant begins by defining three areas of inquiry: logics, physics and ethics. Logic exists unto itself. To be logical, you don’t need to base your thinking on any experience; you only need to develop a coherent thought system. And then there is physics, the natural sciences, and ethics, the science of bringing about good. But on what was morality grounding in? What was the logic that undergirded the way we thought about goodness for instance?
Take, for example, health. Health may seem like it is unconditionally good, but good health can prolong the works of men who put their lives to terrible uses. Health isn’t itself good. Kant came to believe that the only thing unconditionally good is good will, which is willing and wanting good for other people. Kant recognizes that many times there is a disconnect between our choices and what happens in the world of sense. But he says that doesn’t detract from the goodness of your choice. Whatever you do must flow from a motivation that you would like to be universal in all the world. This is how Kant remains relevant today.
Kant gives us some kind of mechanism for understanding why that tension exists and why we can both praise the person and hold them responsible at the same time. It’s making the case that human beings aren’t just pinballs in the universe. I still come across the thought that we don’t have any free will; it’s just an illusion. Everything is just cause and effect within the universe. Kant does a great job of explaining why people think that way but then he takes that extra step and say but that can’t be it because when it’s time for you to decide are you going to lie to someone? You make a choice for yourself.
Kant would come to call the logical undergirding of moral thought the metaphysics of morals. It was sort of like physics there was a since and a logic to it.
Morality, if it were to be stable and trustworthy, must be based on an unchanging moral law as something he called, very famously, the categorical imperative. You are being metaphysically moral if you act in such a way that you wish everybody in the world acted that way all the time. Treating another person is not a means but is an end to himself. Even if society would be better off it’s still wrong to treat them just as instruments for making people happy.