“I agree with you, that Peter Singer does not motivate his account of ideal desires. However, I think there is a way to motivate it as follows: Marquis objects to Singer’s account because he thinks there is an alternative account of ideal desires that is just as plausible as his. But I think Marquis’s account of ideal desires leads to a reductio. If his Marquis’s account is right, then it seems that spiders would have rights to life. This is because if spiders were fully informed and rational, they would desire to live and thus have a right to life. This is analogous to Marquis’s claim that if infants were fully informed and rational they would desire to live and thus have a right life on Singer’s account. But granting spiders the right to life seems absurd. Thus Marquis’s account of ideal desires seems mistaken. However, Singer’s account of ideal desires is not absurd because for Singer, spiders do not have desires at all and hence cannot have ideal desires. Hence, because Singer’s ideal desire account can avoid the reductio, his account is more plausible then Marquis’s. (Obviously this is excluding your Hamlet counterexample, but I am curious what you think about the above.)”
Jury notes correctly that even if this objection is sound then it only addresses my argument that Singer’s account of ideal desires is unmotivated. It does not address the Hamlet counter-example or the other objections I raised.
Nevertheless is worth asking whether Jury’s objection is sound. I do not think it is. Let me offer two responses.
First, even if Marquis’ account of ideal desires is subject to the kind of reduction that Jury mentions, it does not follow that Singer’s account is motivated. I noted in my paper: “Various different conceptions of ideal desires have been proposed which will get around the counter examples aforementioned and not all of them involve the modification of actual desires. Consequently, Singer’s position appears unmotivated.” Here I pointed out there were various different counter examples thatescape the counter examples Singer proposes his account to explain. So, even if one of them fails – the account proposed by Marquis – that does not get around the problem.
Second, I am not convinced Marquis’ account is subject to the reduction Jury mentions. In my paper Boonin on the Sentience Criteria I suggested counter examples like the one suggested by Jury can be dealt with by distinguishing two questions. The first is the question of what an ideally rational self would choose for itself (i.e. the ideally rational self), and what an ideally rational self would choose for it actual self (i.e. his non-ideally rational self).
If one asks the former question then Jury is correct e.g. a spider that had all the rational cognitive capacities of a person, idealised, would not choose to die.
The answer to the second question is not so clear. Here we ask what an ideally rational self would choose if it knew that it would in fact have a future identical with the future of a normal spider – a future existence with no conscious experience at all, where it would lack any ability to value its life or any thing at all. It is certainly not obvious that an ideally rational person would value a future made up of such circumstances.
The question then arises as to which of these two questions is the appropriate one to ask. Thomas Carson argues that is the latter and not the former that is pertinent.
“Suppose I have an irrational fear of dogs. A friend asks me to take care of his dogs while he is away on vacation. My ideally rational self would not fear the dogs and would not hesitate to look after them. Given my intense fear of dogs, however, things are likely to turn out badly if I look after the dogs. Why should I care that my ideal self wouldn’t be afraid of dogs? Wouldn’t it still be foolish for my actual self (with all of its phobias) to take care of the dogs? I might be incapable of adequately caring for them.”
Carson’s point is that something in a person’s future is not necessarily valuable to them if it is something their ideal self would choose for their ideal self – many such choices would be harmful to them. Only if ideal desires are understood in the latter sense can it be plausibly maintained that what a person ideally desires is valuable to them. On the face of it then, it appears that Marquis’ account does not fall prey to the counter example Jury mentions.