Thanks for clearing up the Wilde Reader in Mental Philosophy business. Who does the non-mental philosophy at Oxford?
Despite my occasionally tetchy-tone--how bad our manners become on the internet!--I am honored to have been your interlocutor. (Apostrophe to readers: Colin McGinn is in my opinion one of the most original philosophers in the profession today and, along with Thomas Nagel and John Searle, one of its most forceful and witty writers.) And I am grateful to have been spared having to discuss Foucault, toward whom I feel the same way Charles II felt about his nephew Prince George of Denmark: "I have tried him drunk and I have tried him sober, and I can make nothing of him."
Here is why I agree with you that the question, "What is the best life for me?" is not a scientific one--that is, why it is not a question with a determinate answer one might arrive at by rational reflection. Suppose you are faced with an important life choice. Should I live in the city or the country? Should I go launch my career on Wall Street or at Julliard or in Doctors Without Borders? Should I marry or emulate Don Juan? Should I pour my genius into my life or my work?
There are two possible criteria you might consult in making such choices: objective values and subjective desires. Now, there are plenty of people who think that objective values do not exist, that knowledge, beauty, moral goodness and so forth are only valuable insofar as we desire them. But even if objective values do exist, they are, as Isaiah Berlin never tired of pointing out, irreducibly plural. There is no overarching value that tells us how to trade off x units of beauty against y units of knowledge, or against z units of reduced suffering. Given a choice between two schemes of life that are rich in different values, no rule of maximization dictates the "right" option. So how do you chose? In a cool hour, it comes down to which constellation of objective values appeals more to your taste.
The subjective criterion--consulting our desires--looks more promising at first. When desires conflict, one desire will win out by simply being stronger than others. But desires, unlike objective values, change as a result of our choices. When you decide on a certain course of life, your desires generally rally round over time to endorse that choice retrospectively. If an ambivalent Jones opts for Wall Street over Grub Street, he'll end up preferring that life, but he would have ended up preferring Grub Street had he made that choice. (Then there are those unfortunate people, like Swann in Remembrance of Things Past, whose desires always evolve to condemn their choices retrospectively: They never have what they want or want what they have. Proust called this "soul error.") Since our subjective preferences are largely the product of our choices, they cannot rationally fix those choices. Our lives are underdetermined by our desires the way scientific theories are underdetermined by evidence. Once again, we are driven to the aesthetic.
In such cases of existential indeterminacy, Aristotle recommended choosing a good man as a model. Since we're talking aesthetics, how about a great literary character instead? Some will go for Plato's Socrates, some for Zarathustra, but I'll plump for Mr. Pooter, from the Diary of a Nobody. What could be more noble than struggling like the doughty Pooter, to preserve a little of one's dignity in the face of persistent snubs and humiliations? If life is really a literary narrative, as Alexander Nehama says, then for most of us the genre is not lyric, or epic, or tragedy. It is farce.