Inspired a bit by Ralph's post critiquing Kant's view of unconditioned or fundamental goods, I've been investigating why Kant arrives at his (in my opinion) dissatisfying view that we have only indirect duties to non-human animals. Here's my tentative analysis and conclusion.
Kant begins part I of the Groundwork with his distinction between unconditioned and conditioned goods. He argues that only the rational will is (or is the source of) an unconditioned good. All other goods, including various virtues, such as courage or intelligence; talents and "gifts of nature"; health, wealth, and other "gifts of fortune"; and happiness itself, are conditioned goods. I take Kant to mean by this that their goodness (or perhaps their specifically moral goodness) is only realized when they are accompanied, or exercised by, the good rational will. Indeed, according to Kant, these goods are positively evil “without the basic principles” of a good rational
will to guide them or correct their influence. (G 4:393-4)
In these opening sections of the Groundwork, neither animals nor their welfare are explicitly mentioned. They are mentioned obliquely when Kant later introduces the Formula of Humanity. (G 4:428-29) There Kant reiterates that all “objects of the
inclinations have only a conditional worth” and hence any states of affairs
achieved through action have only conditional worth. Kant then states that “beings the existence of which rests …on nature” or “beings
without reason” have only relative worth, the worth belonging to things, not
persons. Only rational nature,
Kant concludes, has “absolute" or unconditioned worth, so
only our humanity is an “objective end” or an end in itself.
My diagnosis is that animals and their welfare turn out to be conditioned goods within Kant's axiology because this is logically forced upon him by (1) his belief that the rational will alone is an unconditioned good, and (2) his belief that every good is good either unconditionally or conditionally in relation to what is unconditionally good. Since I have Kantian sympathies, I'm disposed to accept (1). So (2) strikes me as the source of the problem. Kant seems to suppose that the unconditioned/conditioned goodness distinction exhausts all possible goods. But animal welfare in particular seems like a counterexample to this. Suppose that Kant is right about (1). Does it follow then that animal welfare is a conditioned good? Only if Kant's distinction is exhaustive. But here's a reason to think it isn't: What characterizes conditioned goods is that their goodness is realized only when accompanied by, or exercised by, the (good) rational will. If the flourishing or suffering of animals is a normatively significant fact —and I've given no direct argument for that claim here — then its significance is not dependent on its relation to the goodness or badness of any rational will. Animal flourishing is good regardless of whether it is the product of any rational willing. Likewise, animal suffering is bad regardless of whether it is the product of any rational willing. I, qua possessor of a rational will, cannot render the flourishing of an animal bad through exercising my will in a particular manner. Nor can I render the suffering of an animal good through exercising my will in a particular manner. (I'm supposing here that non-human animals are not rational wills in Kant's sense.) In contrast then to the other conditioned goods Kant mentions, the value of animal welfare is invariant with respect to rational volition.
If so, then Kant was wrong to suppose that his unconditioned/conditioned goods distinction exhaustively catalogs all goods. Animal welfare is neither an unconditioned good nor a conditioned good with respect to the unconditioned good of the rational will. If a good with these attributes could be made out on a Kantian view, then perhaps animal welfare could be a source of direct duties despite its not being an unconditioned good. Or so I conjecture.