Value-based theorists claim that (in standard cases) whenever it seems that desires provide us with reasons, it is really some valuable feature of the thing desired which provides the normative reason. Ruth Chang, in 'Can Desires Provide Reasons for Action?' (and class last Tuesday), tries to break the dialectical stalemate by discussing a desire for one of two qualitative duplicates, which have all their (intrinsic) features in common.
Think of Buridan's Ass, stuck between two bales of hay, or the ordinary experience of picking a can from the supermarket shelf. It's possible, Chang suggests, for you to just "feel like" one rather than the other, and not for any particular reason. You just feel an affective pull towards that particular object as such, desiring its "thisness" (haecceity or bare identity) rather than any generic feature it happens to exemplify along with the other duplicates.
I don't think this makes much sense, since I don't think haecceities make much sense. But, metaphysics aside, here's a quick counterargument to suggest that these ordinary desires do not, in fact, take bare identities as their objects: we wouldn't care if God secretly switched the duplicates. That wouldn't frustrate one's desire. Having obtained the second can from the left, I now have everything I wanted (so far as cans are concerned, at least). I would not feel in any way cheated to learn that the can has a different 'thisness' from the one I originally set my eyes on. So the 'thisness' could not have been the object of my desire.
(N.B. If you can imagine a case where switching duplicates would bother you, e.g. replacing your wife with a perfect copy, this is arguably because you value the particular causal history connecting you to the one and not the other -- which is just another qualitative feature, albeit a relational one. So there are still no grounds for attributing a desire for bare identity.)
Fortunately, Chang does not need to make such a strong claim. At least if I'm following the dialectic correctly, it should suffice to note that there are no normatively relevant differences between the options in the example, besides the fact that one is desired. (It doesn't matter if the desire is based on some unimportant relational feature rather than being a "feature free" desire for bare identity.)