He offers a partial solution: we may not owe obligations to animals, but we can have obligations in regard to animals that we owe to ourselves. Kant himself grapples with this problem in the Metaphysics of Morals (Kant 1797/2017) although he does not, I think, appreciate its gravity. It is, it seems, an ethical theory for the heartless. It looks as though the theory doesn’t care about suffering at all except in so far as it impairs the rational agency of the sufferer. The problem is that, once you see that the framework (at least at first glance) regards animal suffering as morally irrelevant, the framework as a whole appears callous, inhumane, uninterested in the psychological side of suffering. The problem here is not that the framework has yielded a one-off counterintuitive result. A dog is not the sort of thing that can be wronged. You have not, in Kant’s view, violated any obligations you owe to the dog. There is no room, within Kant’s ethics, for a category of being to which we owe moral obligations even though it is not itself autonomous or bound by moral obligations. Non-human animals are not autonomous in the relevant sense, and they are not moral agents, so they have no fundamental worth. Fundamental worth, for Kant, goes with autonomy and moral agency. Even if Homo sapiens qualifies, non-human animals seem clearly outside the scope of moral obligation. One might wonder whether even members of the species Homo sapiens possess the relevant kind of rationality, which, for Kant, seems to require an incompatibilist form of free will. Kant’s ethics, notoriously, assigns fundamental value to rational beings, where “rational” is understood in an unusually demanding sense.

Kantian moral theory summary