In the wee hours of this morning my eyes popped open, and I spent the next half hour trying to figure out what to write about in this column. After careful, albeit groggy deliberation, I decided to go with free will, both because of the tie-in to New Year's resolutions and because some high-profile scientists have been questioning whether free will exists.

One is the neuroscientist Sam Harris. His new book, The Moral Landscape: How Science Can Determine Human Values (Free Press, 2010), which I critiqued in a previous post, has a section titled "The Illusion of Free Will". Harris argued that "no account of causality leaves room for free will." He cited experiments in which magnetic resonance imaging (MRI) "predicts" that a subject is going to do something—on the basis of activity in the subject's brain—up to 10 seconds before the subject consciously decides to do it.

"Clearly, findings of this kind are difficult to reconcile with the sense that one is the conscious source of one's actions," Harris wrote. This and other experiments, he contended, show that physiological processes of which we are unaware determine our actions; our conscious decisions are literally afterthoughts. "Our belief in free will arises from our moment to moment ignorance of specific prior causes."

In my gloomier moments I have doubts about free will. None of us chooses to be born. We don't choose our parents, our genes, the place of our birth, the circumstances of our upbringing. Nor did our parents have these choices, or theirs, or theirs—ad infinitum. Each moment of our lives is the outcome of a vast web of causes and effects—determined by physical laws—leading back thousands and millions and billions of years to the big bang, the cosmological event that set everything into motion. None of us chooses any of this, so how free can we be?

From this perspective, I can see why Einstein once wrote: "If the moon, in the act of completing its eternal way around the Earth, were gifted with self-consciousness, it would feel thoroughly convinced that it was traveling its way of its own accord…. So would a Being, endowed with higher insight and more perfect intelligence, watching man and his doings, smile about man's illusion that he was acting according to his own free will."

But from another perspective, this rejection of free will makes no sense. Or rather, it goes much too far, because it suggests that our conscious deliberations are epiphenomenal, superfluous, with no real impact on our actions. That is reductionism ad absurdum. As the physicist and Nobel laureate Phil Anderson wrote in his famous 1972 essay, "More Is Different" (pdf), reality has a hierarchical structure with qualitatively different phenomena emerging at different scales: "At each stage entirely new laws, concepts and generalizations are necessary, requiring inspiration and creativity to just as great a degree as in the previous one. Psychology is not applied biology, nor is biology applied chemistry."

Choice is an emergent, psychological phenomenon that cannot be understood in terms of physics and other strictly physical sciences. Our lives pivot around choices big and small. Should I work on this piece on free will this afternoon, or play pond hockey instead? Should I watch more episodes of Dexter tonight or start reading Freedom by Jonathan Franzen? Should I ask my girlfriend to marry me? Should I stop defending Obama from my bitter, disillusioned lefty friends?

Yes, there is much in life that we do not choose. And sometimes we deliberate insincerely toward a foregone conclusion or fail to act on our resolution. But not always. My sleepy decision at 2 A.M. this morning precipitated this essay (although my obsession with free will goes back decades). And I'm unimpressed that if you stuck me in an MRI tube, you'd find "evidence" that my brain "decided" before my conscious self did. Such experiments merely confirm that physiological processes underpin all our perceptions, plans, choices and actions. Only a believer in dualism or an immaterial soul would expect anything else.

Deniers of free will often have weird metaphysical definitions of it, which lead them to view it as a kind of exception to causality. I see free will as roughly equivalent to choice or even (although I hesitate to use this much-abused term) freedom. Moreover, free will is a variable property, which can grow or diminish depending on genetic, neural, experiential, social, political and physical factors. I have more free will—more choices to consider and select from—than I did when I was one or two or 10 years old. I have more free will than adults my age suffering from Alzheimer's, schizophrenia, alcoholism or quadriplegia. I have more than a prisoner in Guantánamo or an illiterate slum-dweller in New Delhi.

Our belief in free will has measurable social benefits. In an experiment recently cited by my fellow SciAm blogger Jesse Bering researchers asked subjects to read a passage written by the Nobel laureate Francis Crick, co-discoverer of the double helix, that cast doubt on free will: "'You,' your joys and your sorrows, your memories and your ambitions, your sense of personal identity and free will, are in fact no more than the behavior of a vast assembly of nerve cells and their associated molecules…. [A]lthough we appear to have free will, in fact, our choices have already been predetermined for us and we cannot change that." Subjects who read this passage were more likely to cheat on a test than control subjects who read a passage about brain science that did not refer to free will.* These results, the researchers concluded, "point to a significant value in believing that free will exists."

Talk about an understatement. Of course belief in free will has value! Free will underpins all our ethics and morality. It forces us to take responsibility for ourselves rather than consigning our fate to our genes or a divine plan. Free will works better than any other single criterion for gauging the vitality of a life or a society. Choices, freely made, are what make life meaningful. Therefore, as New Year's Eve approaches let us all resolve to believe in—and be grateful for—whatever free will we possess.

*Correction (12/28/10): This sentence was edited after posting. It originally stated that subjects who read this passage were more likely to cheat on a test than control subjects who read a passage about brain science that did refer to free will.