In Chapter 2 of GMM, he argues in effect for the claim that if we have free will, if reason can motivate us, then we are bound by the CI. However the claim that we are bound by CI, how can be possible true for every case of our every action? This is what "Kantian ethical philosophy has often been criticized for its dependence on an untenable conception of the freedom of the will. Kant is supposed to have asserted that we are morally responsible for all of our actions because we have free will, and that we have free will because we exist in a noumenal world in which we are uninfluenced by the temptations of desire and inclination."(Kosgaard 159). However I think it cannot be possible because there is implausible that CI works for every case and also human beings are not rational as Kant assumed.
The Possible Problems of Categorical Imperative.
Kant says that "Human capacity to be a moral agent gives each human dignity." This dignity gives unconditional worth to every human being. In this last principle, Kant understands that there is the possibility (or 'capacity') for anyone to act morally, and describes what this action would look like in practice. It explains why we are hesitant to try to put a value on a person's life, and why most people would refuse to even attempt such a thing. For example, money would introduce a 'conditional' value that is not permitted in Kant's view. .
"For other beings such as human beings whose rational capacities govern a will that might be moved by various incentives, temptations, and fears, the representation of something as good or required is not, by itself, sufficient for action. In such beings, the determination by their reason that some option is good or required presents itself as a kind of command as the judgment that they ought to act accordingly (even if they want not to). (Kant 412-414) . .
It is the summary of what he says: We must always act under the practical postulate that our will is free.