I spent this morning pondering whether I should attack neuroscientist Sam Harris for attacking free will. I thought, haven't I spent enough time hassling Harris? I already knocked him, twice, for arguing in The Moral Landscape (Free Press, 2010) that science can help us discover moral principles as true—True with a capital T!—as heliocentrism or Euclid's proof of the Pythagorean theorem. In fact, I have complained about Harris's disparagement of free will in Landscape. Do I really need to revisit the topic?

But Harris keeps intruding on my thoughts, in part because he keeps emailing me about his writings, and especially his new book Free Will (Free Press, 2012). Also, I admit to a certain voyeuristic fascination with Harris. I wonder, what crazy idea is he going to peddle next? Some of his righteous rants give me a perverse pleasure. I'm simultaneously irritated and titillated. I get the same feeling listening to Rush Limbaugh or Rick Santorum.

But I don't know anyone who admires the ideas of Limbaugh or Santorum. Harris's memes, in contrast, are infecting the minds not of right wing and religious cranks but of smart, knowledgeable people. Scientific American columnist Michael Shermer, when he hosted a recent talk by Harris at Caltech, praised him for "cutting through all the obfuscation and getting straight to the point" about free will in his new book. The neurologist Oliver Sacks calls Free Will "brilliant and witty—and never less than incisive." Michael. Oliver. Really?

Harris's new book rates orders of magnitude higher on Amazon's Best Sellers lists than my new book, The End of War (McSweeney's, 2012), which concludes with a chapter called "In Defense of Free Will." That rankles. If I criticize Free Will, will I actually counter Harris's influence or enhance it? Might it look like, or perhaps even be the case, that I'm motivated by base envy rather than a noble desire to defend free will? But how can I not criticize Harris when he's bashing an idea that I cherish? And promoting determinism, a philosophy that I loathe?

Then there's the life's-too-short issue: Harris's new book is only 96 pages, but that's still too long. I don’t have the time—I still haven't done my taxes!—or the inclination to plow through the sort of grimace-inducing reasoning of which Moral Landscape was constructed. Wouldn't my time be better spent whacking New York Times columnist David Brooks for buying the claim of evolutionary psychologists that we are "natural-born killers"? Or riffing on Immortality, the cool new book by Stephen Cave? Or trying to figure out, once and for all, where I stand on fracking?

And what can I say about free will that I haven't said before? Maybe I can just focus on what Harris said at Caltech. He called free will not only an "illusion" but also a "totally incoherent idea" that contradicts what science tells us about how the world works. "The illusoriness of free will," he said, "is as certain a fact, to my mind, as the truth of evolution." This is one of Harris's characteristic traits, flaunting his certitude like a badge of honor.

Harris asks us to consider the case of a serial killer. "Imagine this murderer is discovered to have a brain tumor in the appropriate spot in his brain that could explain his violent impulses. That is obviously exculpatory. We view him as a victim of his biology, and our moral intuitions shift automatically. But I would argue that a brain tumor is just a special case of physical events giving rise to thoughts and actions, and if we fully understood the neurophysiology of any murderer's brain, that would be as exculpatory as finding a tumor in it."

Harris seems to be advancing a reductio ad absurdum, except that he wants us to accept the absurdum: there is no fundamental difference between me and a man compelled to kill by a brain tumor. Or between me and someone who can't help washing his hands every 20 minutes, or someone who's schizophrenic, or a babbling baby, or a newt, or a worm. I mean, if I'm not different from a guy who kills because a tumor provokes him into murderous rages, how am I different from anyone or anything with a brain, no matter how damaged or tiny?

Here's the difference. The man with a tumor has no choice but to do what he does. I do have choices, which I make all the time. Yes, my choices are constrained, by the laws of physics, my genetic inheritance, upbringing and education, the social, cultural, political, and intellectual context of my existence. And as Harris keeps pointing out, I didn't choose to be born into this universe, to my parents, in this nation, at this time. I don’t choose to grow old and die.

But just because my choices are limited doesn't mean they don't exist. Just because I don't have absolute freedom doesn't mean I have no freedom at all. Saying that free will doesn't exist because it isn't absolutely free is like saying truth doesn't exist because we can't achieve absolute, perfect knowledge.

Harris keeps insisting that because all our choices have prior causes, they are not free; they are determined. Of course all our choices are caused. No free-will proponent I know claims otherwise. The question is how are they caused? Harris seems to think that all causes are ultimately physical, and that to hold otherwise puts you in the company of believers in ghosts, souls, gods and other supernatural nonsense.

But the strange and wonderful thing about all organisms, and especially our species, is that mechanistic physical processes somehow give rise to phenomena that are not reducible to or determined by those physical processes. Human brains, in particular, generate human minds, which while subject to physical laws are influenced by non-physical factors, including ideas produced by other minds. These ideas may cause us to change our minds and make decisions that alter the trajectory of our world.

Some of us have a greater capacity to perceive and act on choices than others. The killer with a brain tumor, the schizophrenic, the sociopath, the obsessive-compulsive do not and cannot make decisions--or change their minds--in the way that I do. When I weigh the pros and cons of writing about Harris, my chain of reasoning is determined by the substance of my thoughts, not their physical instantiation.

Consider: When I watch the video of Sam Harris talking at Caltech, is it the electrons streaming through my MacBook, the photons impinging on my eye, the sound waves entering my ear that make me want to respond to Harris? Of course not. It's the meaning of the video that stirs me, not its physical embodiment. I could have watched a DVD of Harris's talk, or read a transcript, or listened to someone summarize his lecture over the telephone. And it's possible that Harris's words, instead of provoking me to write a critical response, could have changed my mind about free will, so that I decided to write a column defending his point of view. Of course, if I thought about it for a moment, I'd realize that the fact that Harris had changed my mind and hence my actions was evidence of my free will.

We are physical creatures, but we are not just physical. We have free will because we are creatures of mind, meaning, ideas, not just matter. Harris perversely--willfully!--refuses to acknowledge this crushingly obvious and fundamental fact about us. He insists that because science cannot figure out the complex causality underpinning free will, it must be illusory. He is a throwback to the old behaviorists, who pretended that subjective, mental phenomena—because they are more difficult to observe and measure than planets and protons—don't exist.

Dwelling on Harris depresses me. All that brainpower and training dedicated to promulgating such bad ideas! He reminds me of one of the brightest students I've ever had, who was possessed by an adamant, unshakable belief in young-earth creationism. I did my best to change his mind, but I never succeeded. I probably won't change the minds of Sam Harris and other hard-core determinists either, but it's worth a shot.