Brains allow organisms to alter their behavior and internal states in response to changes in the environment. The evolution of these structures, tending toward increased size and complexity, has led to vast differences in how the earth's species live.

The human brain responds to information coming from several domains: from the external world, from internal states of the body, and, increasingly, from a sphere of meaning—which includes spoken and written language, social cues, cultural norms, rituals of interaction, assumptions about the rationality of others, judgments of taste and style, etc. Generally, these domains seem unified in our experience: You spot your best friend standing on the street corner looking strangely disheveled. You recognize that she is crying and frantically dialing her cell phone. Did someone assault her? You rush to her side, feeling an acute desire to help. Your "self" seems to stand at the intersection of these lines of input and output. From this point of view, you tend to feel that you are the source of your own thoughts and actions. You decide what to do and not to do. You seem to be an agent acting of your own free will. As we will see, however, this point of view cannot be reconciled with what we know about the human brain.

We are conscious of only a tiny fraction of the information that our brains process in each moment. While we continually notice changes in our experience—in thought, mood, perception, behavior, etc.—we are utterly unaware of the neural events that produce these changes. In fact, by merely glancing at your face or listening to your tone of voice, others are often more aware of your internal states and motivations than you are. And yet most of us still feel that we are the authors of our own thoughts and actions.

All of our behavior can be traced to biological events about which we have no conscious knowledge: this has always suggested that free will is an illusion. For instance, the physiologist Benjamin Libet famously demonstrated that activity in the brain's motor regions can be detected some 350 milliseconds before a person feels that he has decided to move.⁹⁷ Another lab recently used fMRI data to show that some "conscious" decisions can be predicted up to 10 seconds before they enter awareness (long before the preparatory motor activity detected by Libet).⁹⁷ Clearly, findings of this kind are difficult to reconcile with the sense that one is the conscious source of one's actions. Notice that distinction between "higher" and "lower" systems in the brain gets us nowhere: for I no more initiate events in executive regions of my prefrontal cortex than I cause the creaturely outbursts of my limbic system. The truth seems inescapable: I, as the subject of my experience, cannot know what I will next think or do until a thought or intention arises; and thoughts and intentions are caused by physical events and mental stirrings of which I am not aware.

Many scientists and philosophers realized long ago that free will could not be squared with our growing understanding of the physical world.⁹⁸ Nevertheless, many still deny this fact.⁹⁹ The biologist Martin Heisenberg recently observed that some fundamental processes in the brain, like the opening and closing of ion channels and the release of synaptic vesicles, occur at random, and cannot, therefore, be determined by environmental stimuli. Thus, much of our behavior can be considered "self-generated," and therein, he imagines, lies a basis for free will.¹⁰⁰ But "self-generated" in this sense means only that these events originate in the brain. The same can be said for the brain states of a chicken.

If I were to learn that my decision to have a third cup of coffee this morning was due to a random release of neurotransmitters, how could the indeterminacy of the initiating event count as the free exercise of my will? Such indeterminacy, if it were generally effective throughout the brain, would obliterate any semblance of human agency. Imagine what your life would be like if all your actions, intentions, beliefs, and desires were "self-generated" in this way: you would scarcely seem to have a mind at all. You would live as one blown about by an internal wind. Actions, intentions, beliefs, and desires are the sorts of things that can exist only in a system that is significantly constrained by patterns of behavior and the laws of stimulus-response. In fact, the possibility of reasoning with other human beings—or, indeed, of finding their behaviors and utterances comprehensible at all—depends on the assumption that their thoughts and actions will obediently ride the rails of a shared reality. In the limit, Heisenberg's "self-generated" mental events would amount to utter madness.¹⁰¹

The problem is that no account of causality leaves room for free will. Thoughts, moods, and desires of every sort simply spring into view—and move us, or fail to move us, for reasons that are, from a subjective point of view, perfectly inscrutable. Why did I use the term "inscrutable" in the previous sentence? I must confess that I do not know. Was I free to do otherwise? What could such a claim possibly mean? Why, after all, didn't the word "opaque" come to mind? Well, it just didn't—and now that it vies for a place on the page, I find that I am still partial to my original choice. Am I free with respect to this preference? Am I free to feel that "opaque" is the better word, when I just do not feel that it is the better word? Am I free to change my mind? Of course not. It can only change me.

It means nothing to say that a person would have done otherwise had he chosen to do otherwise, because a person's "choices" merely appear in his mental stream as though sprung from the void. In this sense, each of us is like a phenomenological glockenspiel played by an unseen hand. From the perspective of your conscious mind, you are no more responsible for the next thing you think (and therefore do) than you are for the fact that you were born into this world.¹⁰²

Our belief in free will arises from our moment-to-moment ignorance of specific prior causes. The phrase "free will" describes what it feels like to be identified with the content of each thought as it arises in consciousness. Trains of thought like, "What should I get my daughter for her birthday? I know, I'll take her to a pet store and have her pick out some tropical fish," convey the apparent reality of choices, freely made. But from a deeper perspective (speaking both subjectively and objectively), thoughts simply arise (what else could they do?) unauthored and yet author to our actions.

As Daniel Dennett has pointed out, many people confuse determinism with fatalism.¹⁰³ This gives rise to questions like, "If everything is determined, why should I do anything? Why not just sit back and see what happens?" But the fact that our choices depend on prior causes does not mean that they do not matter. If I had not decided to write this book, it wouldn't have written itself. My choice to write it was unquestionably the primary cause of its coming into being. Decisions, intentions, efforts, goals, willpower, etc., are causal states of the brain, leading to specific behaviors, and behaviors lead to outcomes in the world. Human choice, therefore, is as important as fanciers of free will believe. And to "just sit back and see what happens" is itself a choice that will produce its own consequences. It is also extremely difficult to do: just try staying in bed all day waiting for something to happen; you will find yourself assailed by the impulse to get up and do something, which will require increasingly heroic efforts to resist.

Of course, there is a distinction between voluntary and involuntary actions, but it does nothing to support the common idea of free will (nor does it depend upon it). The former are associated with felt intentions (desires, goals, expectations, etc.) while the latter are not. All of the conventional distinctions we like to make between degrees of intent—from the bizarre neurological complaint of alien hand syndrome¹⁰⁴ to the premeditated actions of a sniper—can be maintained: for they simply describe what else was arising in the mind at the time an action occurred. A voluntary action is accompanied by the felt intention to carry it out, while an involuntary action isn't. Where our intentions themselves come from, however, and what determines their character in every instant, remains perfectly mysterious in subjective terms. Our sense of free will arises from a failure to appreciate this fact: we do not know what we will intend to do until the intention itself arises. To see this is to realize that you are not the author of your thoughts and actions in the way that people generally suppose. This insight does not make social and political freedom any less important, however. The freedom to do what one intends, and not to do otherwise, is no less valuable than it ever was.

The question of free will is no mere curio of philosophy seminars. The belief in free will underwrites both the religious notion of "sin" and our enduring commitment to retributive justice.¹⁰⁵ The Supreme Court has called free will a "universal and persistent" foundation for our system of law, distinct from "a deterministic view of human conduct that is inconsistent with the underlying precepts of our criminal justice system" (United States v. Grayson, 1978).106 Any scientific developments that threatened our notion of free will would seem to put the ethics of punishing people for their bad behavior in question.¹⁰⁷

But, of course, human goodness and human evil are the product of natural events. The great worry is that any honest discussion of the underlying causes of human behavior seems to erode the notion of moral responsibility. If we view people as neuronal weather patterns, how can we coherently speak about morality? And if we remain committed to seeing people as people, some who can be reasoned with and some who cannot, it seems that we must find some notion of personal responsibility that fits the facts.

What does it really mean to take responsibility for an action? For instance, yesterday I went to the market; as it turns out, I was fully clothed, did not steal anything, and did not buy anchovies. To say that I was responsible for my behavior is simply to say that what I did was sufficiently in keeping with my thoughts, intentions, beliefs, and desires to be considered an extension of them. If, on the other hand, I had found myself standing in the market naked, intent upon stealing as many tins of anchovies as I could carry, this behavior would be totally out of character; I would feel that I was not in my right mind, or that I was otherwise not responsible for my actions. Judgments of responsibility, therefore, depend upon the overall complexion of one's mind, not on the metaphysics of mental cause and effect.

Consider the following examples of human violence:

1. A four-year-old boy was playing with his father's gun and killed a young woman. The gun had been kept loaded and unsecured in a dresser drawer.
2. A twelve-year-old boy, who had been the victim of continuous physical and emotional abuse, took his father's gun and intentionally shot and killed a young woman because she was teasing him.
3. A twenty-five-year-old man, who had been the victim of continuous abuse as a child, intentionally shot and killed his girlfriend because she left him for another man.
4. A twenty-five-year-old man, who had been raised by wonderful parents and never abused, intentionally shot and killed a young woman he had never met "just for the fun of it."
5. A twenty-five-year-old man, who had been raised by wonderful parents and never abused, intentionally shot and killed a young woman he had never met "just for the fun of it." An MRI of the man's brain revealed a tumor the size of a golf ball in his medial prefrontal cortex (a region responsible for the control of emotion and behavioral impulses).

In each case a young woman has died, and in each case her death was the result of events arising in the brain of another human being. The degree of moral outrage we feel clearly depends on the background conditions described in each case. We suspect that a four-year-old child cannot truly intend to kill someone and that the intentions of a twelve year-old do not run as deep as those of an adult. In both cases 1 and 2, we know that the brain of the killer has not fully matured and that all the responsibilities of personhood have not yet been conferred. The history of abuse and precipitating circumstance in example 3 seem to mitigate the man's guilt: this was a crime of passion committed by a person who had himself suffered at the hands of others. In 4, we have no abuse, and the motive brands the perpetrator a psychopath. In 5, we appear to have the same psychopathic behavior and motive, but a brain tumor somehow changes the moral calculus entirely: given its location in the MPFC, it seems to divest the killer of all responsibility. How can we make sense of these gradations of moral blame when brains and their background influences are, in every case, and to exactly the same degree, the real cause of a woman's death?

It seems to me that we need not have any illusions about a casual agent living within the human mind to condemn such a mind as unethical, negligent, or even evil, and therefore liable to occasion further harm. What we condemn in another person is the intention to do harm—and thus any condition or circumstance (e.g., accident, mental illness, youth) that makes it unlikely that a person could harbor such an intention would mitigate guilt, without any recourse to notions of free will. Likewise, degrees of guilt could be judged, as they are now, by reference to the facts of the case: the personality of the accused, his prior offenses, his patterns of association with others, his use of intoxicants, his confessed intentions with regard to the victim, etc. If a person's actions seem to have been entirely out of character, this will influence our sense of the risk he now poses to others. If the accused appears unrepentant and anxious to kill again, we need entertain no notions of free will to consider him a danger to society.

Of course, we hold one another accountable for more than those actions that we consciously plan, because most voluntary behavior comes about without explicit planning.¹⁰⁸ But why is the conscious decision to do another person harm particularly blameworthy? Because consciousness is, among other things, the context in which our intentions become completely available to us. What we do subsequent to conscious planning tends to most fully reflect the global properties of our minds—our beliefs, desires, goals, prejudices, etc. If, after weeks of deliberation, library research, and debate with your friends, you still decide to kill the king—well, then killing the king really reflects the sort of person you are. Consequently, it makes sense for the rest of society to worry about you.

While viewing human beings as forces of nature does not prevent us from thinking in terms of moral responsibility, it does call the logic of retribution into question. Clearly, we need to build prisons for people who are intent upon harming others. But if we could incarcerate earthquakes and hurricanes for their crimes, we would build prisons for them as well.¹⁰⁹ The men and women on death row have some combination of bad genes, bad parents, bad ideas, and bad luck — which of these quantities, exactly, were they responsible for? No human being stands as author to his own genes or his upbringing, and yet we have every reason to believe that these factors determine his character throughout life. Our system of justice should reflect our understanding that each of us could have been dealt a very different hand in life. In fact, it seems immoral not to recognize just how much luck is involved in morality itself.

Consider what would happen if we discovered a cure for human evil. Imagine, for the sake of argument, that every relevant change in the human brain can be made cheaply, painlessly, and safely. The cure for psychopathy can be put directly into the food supply like vitamin D. Evil is now nothing more than a nutritional deficiency.

If we imagine that a cure for evil exists, we can see that our retributive impulse is profoundly flawed. Consider, for instance, the prospect of withholding the cure for evil from a murderer as part of his punishment. Would this make any moral sense at all? What could it possibly mean to say that a person deserves to have this treatment withheld? What if the treatment had been available prior to the person's crime? Would he still be responsible for his actions? It seems far more likely that those who had been aware of his case would be indicted for negligence. Would it make any sense at all to deny surgery to the man in example 5 as a punishment if we knew the brain tumor was the proximate cause of his violence? Of course not. The urge for retribution, therefore, seems to depend upon our not seeing the underlying causes of human behavior.

Despite our attachment to notions of free will, most us know that disorders of the brain can trump the best intentions of the mind. This shift in understanding represents progress toward a deeper, more consistent, and more compassionate view of our common humanity — and we should note that this is progress away from religious metaphysics. It seems to me that few concepts have offered greater scope for human cruelty than the idea of an immortal soul that stands independent of all material influences, ranging from genes to economic systems.

And yet one of the fears surrounding our progress in neuroscience is that this knowledge will dehumanize us. Could thinking about the mind as the product of the physical brain diminish our compassion for one another? While it is reasonable to ask this question, it seems to me that, on balance, soul/body dualism has been the enemy of compassion. For instance, the moral stigma that still surrounds disorders of mood and cognition seems largely the result of viewing the mind as distinct from the brain. When the pancreas fails to produce insulin, there is no shame in taking synthetic insulin to compensate for its lost function. Many people do not feel the same way about regulating mood with antidepressants (for reasons that appear quite distinct from any concern about potential side effects). If this bias has diminished in recent years, it has been because of an increased appreciation of the brain as a physical organ.

However, the issue of retribution is a genuinely tricky one. In a fascinating article in The New Yorker, Jared Diamond recently wrote of the high price we often pay for leaving vengeance to the state.¹¹⁰ He compares the experience of his friend Daniel, a New Guinea highlander, who avenged the death of a paternal uncle and felt exquisite relief, to the tragic experience of his late father-in-law, who had the opportunity to kill the man who murdered his family during the Holocaust but opted instead to turn him over to the police. After spending only a year in jail, the killer was released, and Diamond's father-in-law spent the last sixty years of his life "tormented by regret and guilt." While there is much to be said against the vendetta culture of the New Guinea Highlands, it is clear that the practice of taking vengeance answers to a common psychological need.

We are deeply disposed to perceive people as the authors of their actions, to hold them responsible for the wrongs they do us, and to feel that these debts must be repaid. Often, the only compensation that seems appropriate requires that the perpetrator of a crime suffer or forfeit his life. It remains to be seen how the best system of justice would steward these impulses. Clearly, a full account of the causes of human behavior should undermine our natural response to injustice, at least to some degree. It seems doubtful, for instance, that Diamond's father-in-law would have suffered the same pangs of unrequited vengeance if his family had been trampled by an elephant or laid low by cholera. Similarly, we can expect that his regret would have been significantly eased if he had learned that his family's killer had lived a flawlessly moral life until a virus began ravaging his medial prefrontal cortex.

It may be that a sham form of retribution could still be moral, if it led people to behave far better than they otherwise would. Whether it is useful to emphasize the punishment of certain criminals — rather than their containment or rehabilitation — is a question for social and psychological science. But it seems quite clear that a retributive impulse, based upon the idea that each person is the free author of his thoughts and actions, rests on a cognitive and emotional illusion — and perpetuates a moral one.

It is generally argued that our sense of free will presents a compelling mystery: on the one hand, it is impossible to make sense of it in causal terms; on the other, there is a powerful subjective sense that we are the authors of our own actions.¹¹¹ However, I think that this mystery is itself a symptom of our confusion. It is not that free will is simply an illusion: our experience is not merely delivering a distorted view of reality; rather, we are mistaken about the nature of our experience. We do not feel as free as we think we feel. Our sense of our own freedom results from our not paying attention to what it is actually like to be what we are. The moment we do pay attention, we begin to see that free will is nowhere to be found, and our subjectivity is perfectly compatible with this truth. Thoughts and intentions simply arise in the mind. What else could they do? The truth about us is stranger than many suppose: The illusion of free will is itself an illusion.

94. Bowles, 2006, 2008, 2009.
95. Churchland, 2008a.
96. Libet, Gleason, Wright, & Pearl, 1983.
97. Soon, Brass, Heinze, & Haynes, 2008. Libet later argued that while we don't have free will with respect to initiating behavior, we might have free will to veto an intention before it becomes effective (Libet, 1999, 2003). I think his reasoning was clearly flawed, as there is every reason to think that a conscious veto must also arise on the basis of unconscious neural events.
98. Fisher, 2001; Wegner, 2002; Wegner, 2004.
99. Heisenberg, 2009; Kandel, 2008; Karczmar, 2001; Libet, 1999; McCrone, 2003; Planck & Murphy, 1932; Searle, 2001; Sperry, 1976.
100. Heisenberg, 2009.
101. One problem with this approach is that quantum mechanical effects are probably not, as a general rule, biologically salient. Quantum effects do drive evolution, as high-energy particles like cosmic rays cause point mutations in DNA and the behavior of such particles passing through the nucleus of a cell is governed by the laws of quantum mechanics. Evolution, therefore, seems unpredictable in principle (Silver, 2006).
102. The laws of nature do not strike most of us as incompatible with free will because we have not imagined how human action would appear if all cause-and-effect relationships were understood. But imagine that a mad scientist has developed a means of controlling the human brain at a distance: What would it be like to watch him send a person to and fro on the wings of her "will"? Would there be even the slightest temptation to impute freedom to her? No. But this mad scientist is nothing more than causal determinism personified. What makes his existence so inimical to our notion of free will is that when we imagine him lurking behind a person's thoughts and actions — tweaking electrical potentials, manufacturing neurotransmitters, regulating genes, etc. — we cannot help but let our notions of freedom and responsibility travel up the puppet's strings to the hand that controls them. To see that the addition of randomness does nothing to change this situation, we need only imagine the scientist basing the inputs to his machine on a shrewd arrangement of roulette wheels. How would such unpredictable changes in the states of a person's brain constitute freedom?

Swapping any combination of randomness and natural law for a mad scientist. we can see that all the relevant features of a person's inner life would be conserved—thoughts, moods, and intentions would still arise and beget actions—and yet we are left with the undeniable fact that the conscious mind cannot be the source of its own thoughts and intentions. This discloses the real mystery of free will: if our experience is compatible with its utter absence, how can we say that we see any evidence for it in the first place?
103. Dennett, 2003.
104. The phrase "alien hand syndrome" describes a variety of neurological disorders in which a person no longer recognizes ownership of one of his hands. Actions of the nondominant hand in the split-brain patient can have this character, and in the acute phase after surgery this can lead to overt, intermanual conflict. Zaidel et al. (2003) prefer the phrase "autonomous hand," as patients typically experience their hand to be out of control but do not ascribe ownership of it to someone else. Similar anomalies can be attributed to other neurological causes: for instance, in sensory alien hand syndrome (following a stroke in the right posterior cerebral artery) the right arm will sometimes choke or otherwise attack the left side of the body (Pryse-Philips, 2003).
105. See S. Harris, 2004, pp. 272-274.
106. Burns & Bechara, 2007, p. 264.
107. Others have made a similar argument. See Burns & Bechara, 2007, p. 264; J. Greene & Cohen, 2004, p. 1776.
108. Cf. Levy, 2007.
109. The neuroscientist Michael Gazzaniga writes:

Neuroscience will never find the brain correlate of responsibility, because that is something we ascribe to humans—to people—not to brains. It is a moral value we demand of our fellow, rule-following human beings. Just as optometrists can tell us how much vision a person has (20/20 or 20/200) but cannot tell us when someone is legally blind or has too little vision to drive a school bus, so psychiatrists and brain scientists might be able to tell us what someone's mental state or brain condition is but cannot tell us (without being arbitrary) when someone has too little control to be held responsible. The issue of responsibility (like the issue of who can drive school buses) is a social choice. In neuroscientific terms, no person is more or less responsible than any other for actions. We are all part of a deterministic system that someday, in theory, we will completely understand. Yet the idea of responsibility, a social construct that exists in the rules of a society, does not exist in the neuronal structures of the brain (Gazzaniga, 2005, pp. 101-102).

While it is true that responsibility is a social construct attributed to people and not to brains, it is a social construct that can make more or less sense given certain facts about a person's brain. I think we can easily imagine discoveries in neuroscience, as well as brain imaging technology, that would allow us to attribute responsibility to persons in a far more precise way than we do at present. A "Twinkie defense" would be entirely uncontroversial if we learned that there was something in the creamy center of every Twinkie that obliterated the frontal lobe's inhibitory control over the limbic system.

But perhaps "responsibility" is simply the wrong construct: for Gazzaniga is surely correct to say that "in neuroscientific terms, no person is more or less responsible than any other for actions." Conscious actions arise on the basis of neural events of which we are not conscious. Whether they are predictable or not, we do not cause our causes.
110. Diamond, 2008.
111. In the philosophical literature, one finds three approaches to the problem: determinism, libertarianism, and compatibilism. Both determinism and libertarianism are often referred to as "incompatibilist" views, in that both maintain that if our behavior is fully determined by background causes, free will is an illusion. Determinists believe that we live in precisely such a world; libertarians (no relation to the political view that goes by this name) believe that our agency rises above the field of prior causes—and they inevitably invoke some metaphysical entity, like a soul, as the vehicle for our freely acting wills. Compatibilists, like Daniel Dennett, maintain that free will is compatible with causal determinism (see Dennett, 2003; for other compatibilist arguments see Ayer, Chisholm, Strawson, Frankfurt, Dennett, and Watson — all in Watson, 1982). The problem with compatibilism, as I see it, is that it tends to ignore that people's moral intuitions are driven by deeper, metaphysical notions of free will. That is, the free will that people presume for themselves and readily attribute to others (whether or not this freedom is, in Dennett's sense, "worth wanting") is a freedom that slips the influence of impersonal, background causes. The moment you show that such causes are effective—as any detailed account of the neurophysiology of human thought and behavior would—proponents of free will can no longer locate a plausible hook upon which to hang their notions of moral responsibility. The neuroscientists Joshua Greene and Jonathan Cohen make the same point:

Most people's view of the mind is implicitly dualist and libertarian and no: materialist and compatibilist . . . [I]ntuitive free will is libertarian, not compatibilist. That is, it requires the rejection of determinism and an implicit commitment to some kind of magical mental causation . . . contrary to legal and philosophical orthodoxy, determinism really does threaten free will and responsibility as we intuitively understand them (J. Greene & Cohen, 2004. pp. 1779-1780).