 Of course, even were we to agree with Kant that ethics should begin with analysis, and that analysis is or should be an entirely a priori undertaking, this would not explain why all of the fundamental questions of moral philosophy must be pursued a priori. Indeed, one of the most important projects of moral philosophy, for Kant, is to show that we, as rational agents, are bound by moral requirements and that fully rational agents would necessarily comply with them. Kant admits that his analytical arguments for the CI are inadequate on their own because the most they can show is that the CI is the supreme principle of morality if there is such a principle. Kant must therefore address the possibility that morality itself is an illusion by showing that the CI really is an unconditional requirement of reason that applies to us. Even though Kant thought that this project of “establishing” the CI must also be carried out a priori, he did not think we could pursue this project simply by analyzing our moral concepts or examining the actual behavior of others. What is needed, instead, is a “synthetic”, but still a priori, kind of argument that starts from ideas of freedom and rational agency and critically examines the nature and limits of these capacities.