In "The Good Life: A Defense of Attitudinal Hedonism," Fred Feldman discusses hedonism, which is the thought that for a life to go well for the one who experiences it is a matter of enjoyment. He goes on to distinguish the several forms of hedonism, considers several classical objections, and argues that these objections are irrelevant to the form of hedonism that he puts forth. Feldman specifically discusses attitudinal pleasure which he defines to be a mode of consciousness or being aware of a state of things that takes place among other attitudes, such as hope and fear. Feldman's concern is not goodness in itself nor morality, but rather value of a life for the person living that life. His version of intrinsic attitudinal hedonism (IAH) is that it is the "view that the value of a person's life is determined by the total amount of intrinsic attitudinal pleasure the person enjoys during that life". One objection given to this view is put forth by Shelly Kagan:
P1. Hedonism implies that what determines the quality of a person's life is something completely internal to that person, i.e. in the mind of that person.
C1. Thus, hedonism is a "mental statism."
P2. Hedonism, like all forms of mental statism, implies that if two lives are alike with respect to mental states, they must also be alike with respect to pleasures and pains, then those lives are of equal value.
P3. Thus, P2 remains true even if one of the individuals takes pleasure from correctly perceived interaction with real human beings, and the other individual is merely a brain in a vat, not actually perceiving a real life.
P4. The real human being and the brain in the vat do not, or cannot, have lives of equal value.
C. Therefore, hedonism does not adequately represent the value of a life.
Feldman addresses Kagan's argument and a similar case put forth by Tom Nagel, by slightly modifying the IAH view to take in consideration the true state of affairs, thus eliminating the entire argument because the real person who is experiencing the true state of affairs would still have a life with more value than the brain in a vat that only thinks it is experiencing a 'real' life.
I do agree with Feldman that some sort of hedonism seems to represent how people find value in their lives, however, I'm not sure he needed to modify his view in order to satisfy Kagan's argument since value of one's life to one's self is truly in the mind of that person experiencing it. Thus, both the real human being and the brain in the vat were satisfied with their lives even though only the real human was actually having true experiences. But if we look at from the perspective of the person with the life, both are having satisfactory lives to which they would feel that are of equal value to any other life. So, only to outsiders do the lives not seem equally valuable, but I don't think that really matters because you only experience your own life.
Feldman, Fred. "The Good Life: A Defense of Attitudinal Hedonism." Ethical Theory: An Anthology. Ed. Russ Shafer-Landau. Blackwell Publishing Ltd, 2007. 294-305. Print.