How the Categorical Imperative Entails that we cannot Treat Animals as Means Only

It is often thought that utilitarianism is the only moral theory that recognizes that non-rational animals matter morally. This view is usually contrasted with some deontological view (typically Kant) that claims that animals in no way matter. But this is actually mistaken.

Kant’s first formulation of the Categorical Imerpative ‘Act on the maxim which you can will as a universal law of nature’ straightforwardly leads to his second formulation ‘act so as to treat the humanity in a person as an end only and never as a means only’. This is because I cannot consistently will a maxim that lets rational agents be treated as means only, as that would mean that I, a rational agent, could be treated as a means only which contradicts the natural desire of rational agents to govern themselves. Exactly parralell reasoning will get you another formulation of the categorical imperative which is something like ‘act so as to treat sentient creatures as an end only and never as a means only’; for consider a world in which sentient creatures were treated as a means only (used for food, hunted for pleasure, etc) in such a world it would be OK to treat you as a means to an end, (you are after all a sentient being), but this contradicts a sentient being’s natural desire not to be used in such ways.

Perhaps one may object that they could will a maxim which was limited to non-rational sentient beings. But then you have the usual problems with infants, the mentally infirm, and senile senior citizens. Perhaps we could limit it to non-human sentient beings? But this is to make an exception to a universal rule, which is the very indication that one is acting contrary to the Categorical Imperative!