What does it mean to talk of individual interests or welfare? To expand on my earlier post, I think we need to distinguish descriptive and normative concepts in this vicinity. For example, there's a purely description notion of biological interests or natural "flourishing" that has no inherent normative significance (at least prima facie). On the other hand, I suggested, we can understand a genuinely normative sense of 'interests' as meaning something like what's desirable for the sake of an individual (where being 'desirable for the sake of S' does not immediately entail being desirable tout court). This requires some clarification.
For one thing: talk of X being 'desirable for the sake of S' naturally suggests the following two-part interpretation: (i) you have reason to desire X, and (ii) S is the normative source of this reason.
But this interpretation is no good, for it makes it impossible to express non-benevolent views like egoism, according to which we have no reason to care about others' interests. Such views may be false, but they should at least be coherently expressible. So we had better not analyze 'interests' in such a way as to rule out egoism from the start. Instead, we need to pin down the sense in which an egoist might allow that X is - or would be - "desirable for S's sake", without thereby committing himself to thinking that he, personally, has any reason to want it.
A promising answer, I think, is to combine the modal and normative senses of 'desirable'. The modal sense means "can be desired". The normative sense means "should be desired" -- or at least that there's some reason to desire the object. The hybrid view I have in mind thus concerns whether there can be reason to desire X for S's sake (i.e., at least for agents who care about S). This seems to solve the problem: an egoist can agree that anyone who cares about S thereby [for S's sake] has a reason to desire X, without thereby committing himself to having such reasons, since he personally may not care about S. (This analysis also seems to satisfy the other desideratum motivating my previous post, namely, that plants and other non-sentients don't have normative interests. Even if you care about plants, they just aren't capable of sourcing reasons in this way. You may have reason to tend to your garden, but it will be for your own sake, rather than the plants'.)
But now consider a second puzzle: mightn't we act for another's sake, in a way that's independent of the other's welfare? I especially have in mind symbolic acts expressing "respect" for another's deepest concerns. Once we recognize the distinction between 'Good To' and 'Good For', the following possibility arises: I might, out of respect for S, be motivated to promote some end that is a good to her (i.e. something she values), though it is not good (or bad) for her.
For example, suppose Sally cares passionately about philosophy. After Sally dies, Bob might honour Sally's memory by making a donation to promote philosophical education. He does not thereby think that he is making Sally better off. (She's dead, and even if we accept a 'success theory' of welfare that allows for posthumous benefits, we can stipulate that this action doesn't affect the success of Sally's life efforts.) Nevertheless, there seems a clear sense in which he's acting for Sally's sake. Is this a counterexample to my analysis?
Maybe. I'm not entirely sure what to think of this, so I'd welcome your thoughts. Here's a tentative response: perhaps Bob is like the gardener. Although motivated by considerations outside of himself (plants, or Sally's memory), those considerations aren't really capable of sourcing reasons, so any reason for Bob to so act instead stems from elsewhere (perhaps from Bob himself). Consider the question: 'Why is it good for Bob to honour Sally's memory in this way -- who benefits?' We may think this is just another way of asking, for whose sake does the reason exert its normative force? And the answer is presumably not 'Sally', since we have already stipulated that she does not benefit posthumously. It might be 'Bob', or it might be 'the world as a whole' (on this view: such moral acts make the world a better place, independently of the welfare of the individuals in it).
A third and final puzzle: mightn't we have reasons to act for the sakes of impersonal entities? I can easily imagine being motivated by my love of philosophy, for example. And it seems plausible that such acts will often be normatively justified. But wouldn't it seem a category mistake to say that the discipline of philosophy has welfare interests? Perhaps. But we may doubt that my motivating reason is itself the normative reason here. As in the case of Bob, it might instead be that any normative reason in this case is sourced either in myself, or in 'the world as whole'.
Even so, isn't 'the world as a whole' itself an impersonal entity? So if I think it might ultimately ground moral reasons, doesn't my earlier analysis then imply that the world has interests? This seems very strange. But then, 'the world' is an odd sort of entity. It might be better to instead say that such reasons rely on no particular (contingent) source at all, so that talk of 'the world' here is just a verbal convenience. (As the term 'zero' illustrates, it can be useful to talk of nothing as a kind of something, so long as we are careful not to be misled.) For a reason to exert its normative force 'for the sake of the world' is just for the reason to exert brute normative force, without needing this to be "grounded" in anything else (in particular, the interests of any being).
But I'm not sure how plausible this all sounds...