Only science can help us answer these questions, he says. That’s because truths about morality and meaning must “relate to facts about the well-being of conscious creatures,” and science alone — especially neuroscience, his field — can uncover those facts. So rather than consulting Aristotle or Kant (let alone the Bible or the Koran) about what is necessary for humans to flourish, why not go to the sciences that study conscious mental life? ...I think Appiah hits the nail on the head, or at least this was exactly the problem I saw in Harris's Spring TED talk. If the book really does say only science is needed to grasp right and wrong, good and bad etc, my guess is that Harris is simplifying because he's writing a polemic. His purpose it to combat the belief that religion is authoritative about moral matters and he writes for a public that respects religion first, science second, and philosophy not much. So "only science" might be a strategic answer.
But wait: how do we know that the morally right act is, as Harris posits, the one that does the most to increase well-being, defined in terms of our conscious states of mind? Has science really revealed that? If it hasn’t, then the premise of Harris’s all-we-need-is-science argument must have nonscientific origins.
In fact, what he ends up endorsing is something very like utilitarianism, a philosophical position that is now more than two centuries old, and that faces a battery of familiar problems. Even if you accept the basic premise, how do you compare the well-being of different people? Should we aim to increase average well-being (which would mean that a world consisting of one bliss case is better than one with a billion just slightly less blissful people)? Or should we go for a cumulative total of well-being (which might favor a world with zillions of people whose lives are just barely worth living)? If the mental states of conscious beings are what matter, what’s wrong with killing someone in his sleep? How should we weigh present well-being against future well-being?
It’s not that Harris is unaware of these questions, exactly. He refers to the work of Derek Parfit, who has done more than any philosopher alive to explore such difficulties. But having acknowledged some of these complications, he is inclined to push them aside and continue down his path.
That’s the case even with something as basic as what’s meant by well-being. Harris often writes as if all that matters is our conscious experience. Yet he also insists that truth is an important value. So does it count against your well-being if your happiness is based on an illusion — say, the false belief that your wife loves you? Or is subjective experience all that matters, in which case a situation in which the husband is fooled, and the wife gets pleasure from fooling him, is morally preferable to one in which she acknowledges the truth? Harris never articulates his central claim clearly enough to let us know where he would come down. But if he thinks that well-being has an objective component, one wants to know how science revealed this fact.
Then again, Harris could be just plain confused. If you think moral facts supervene on physical facts, you might erroneously conclude that they can best be investigated by experts on the relevant physical facts. But which physical facts are relevant? Sadly, you just aren't going to know before "doing" a lot of ethics to find out the precise contours of the moral facts.
But I'm getting ahead of myself. More on Harris after I've read the book.