Immanuel Kant argued that morality requires us to act on principles that we can will as universal laws. However, there has always been profound disagreement about how to apply this requirement, and about why this demand should be morally fundamental. This dissertation offers new answers to these questions by developing a deeper understanding of the “practical” principles that Kant wants us to be able to will as universal laws.

My primary thesis is that practical principles state three things: a reason to act, the end or goal that this reason requires us to accomplish, and the means that we must use to achieve that end. Several crucial lines of Kant’s thought require this structure for practical principles, I argue. Primarily: practical principles, as principles for action, must also be causal principles, and Kant’s views on causation require practical principles to have the structure I propose.

I use this structure to answer some venerable problems: first, why can’t we will any principle whatsoever as a universal law, especially if we make each principle unique to each case? Because Kant requires causal relations to be rule-governed, I argue, in a way that prevents practical principles from being unique to each situation.

Next, why isn’t morality satisfied when everyone could follow our principles? Under my interpretation, practical principles say how we are required to act. As rational beings, though, we cannot be required to contradict ourselves. Everyone could contradict themselves in order to follow a principle, but we cannot be required to do so. So I argue that “willing” our principles as universal laws is supposed to capture how principles cannot require us to contradict ourselves.

Last, why must we act on principles that we can will as universal laws? Kant answers: to act that way is to give laws to ourselves, and we must think of ourselves as laws to ourselves. That is autonomy. But if I give a law to myself, couldn’t I release myself from that law, too? I conclude by using my interpretation to explain how laws that we give to ourselves can also impose genuine requirements on us.