On free will-14: Misuse of the insanity defense

(For previous posts in this series, see here.)

Many people are suspicious of the insanity defense, suspecting that it is abused by unscrupulous criminals and their lawyers. The fact that psychiatrists and other experts can be found to argue both sides of the case adds weight to the suspicion that there is no objective basis to many of the claims of insanity.

This problem arose when the grounds for the insanity defense was loosened from the strict M’Naghten rule. In a 1954 court decision Durham vs. United States, a US Appeals Court extended the reach of the insanity defense beyond cognitive incapacity and said that “The rule we now hold is simply that the accused is not criminally responsible if his unlawful act was the product of mental disease or mental defect.” (Steven Pinker, The Blank Slate, p. 184) As a result of the Durham precedent, there was a proliferation of expert testimony on both sides to argue the question of whether the accused did in fact have a mental disease or defect and whether the act that was committed was the product of that defective mental state, and thus not truly ‘free’.

The Durham standard is grounded in the idea of free will and assumes that in general everyone has free will to choose between right and wrong but for some people their brain defects prevent them from being able to make such choices. If it can be shown that someone’s actions are due to compulsions beyond their control, then they should not be held responsible for their actions since their will was not free. For example, lawyers in defense cases may sometimes concede that their clients did commit the crime and were aware that it was wrong (thus failing to meet the M’Naghten threshold), but they should not be held responsible because the ultimate cause of their action lay in childhood abuse or addiction to drugs or alcohol or violence in the media or rock music or pornography or the pressures of society at large, resulting in them having a defective mental state. Since it was this defective mental state that caused them to act in this way, it is argued that they were not acting freely and thus should not be held responsible for their actions.

One consequence of the understanding that there is no such thing as free will and that the purpose of punishment is deterrence and not moral judgment is that mental ‘defects’ by themselves (whatever their cause) are not sufficient to absolve people of responsibility for their actions, because every criminal act is always due to that person’s brain being different from the norm, and thus defective in some way. As Pinker says (p. 184), “Unless one believes that ordinary acts are chosen by a ghost in the machine, all acts are products of cognitive and emotional systems in the brain. Criminal acts are relatively rare – if everyone in a defendant’s shoes acted as he did, the law against what he did would be repealed – so heinous acts will often be products of a brain system that is in some way different from the norm, and the behavior can be construed as “a product of mental disease or mental defect:'” Hence the mere fact of a brain defect being the cause of an act should not be a defense.

The problem with the Durham rule is that, as a result of belief in free will, it mixes up explanation with exculpation. If we give up on the idea of free will, the legal process actually gets simpler. As Anthony Cashmore says, “psychiatrists and other experts on human behavior should be eliminated from the initial judicial proceedings—the role of the jury would be to simply determine whether or not the defendant was guilty of committing the crime; the mental state of the defendant would play no part in this decision. However, if a defendant were found guilty, then a court-appointed panel of experts would play a role in advising on matters of punishment and treatment.” Pinker adds:

And this explains why the usual exemptions from responsibility should not be granted to all males or all abuse victims or all of humanity, even when we think we can explain what led them to act as they did. The explanations may help us understand the parts of the brain that made a behavior tempting, but they say nothing about the other parts of the brain (primarily in the prefrontal cortex) that could have inhibited the behavior by anticipating how the community would respond to it. We are that community, and our major lever of influence consists in appealing to that inhibitory brain system. Why should we discard our lever on the system for inhibition just because we are coming to understand the system for temptation? If you believe we shouldn’t, that is enough to hold people responsible for their actions – without appealing to a will, a soul, a self, or any other ghost in the machine. (p. 183)

When we punish people for crimes, it should be solely for the purpose of deterring them and others from committing those same crimes in the future. The idea of punishment as a deterrent to crime makes sense even in the absence of free will but to be effective as such, punishments must be applied consistently. As Justice Oliver Wendell Holmes said (Pinker, p. 181), “If I were having a philosophical talk with a man I was going to have hanged (or electrocuted) I should say, ‘I don’t doubt that your act was inevitable for you but to make it more avoidable by others we propose to sacrifice you to the common good. You may regard yourself as a soldier dying for your country if you like. But the law must keep its promises.’ ” Note that while this example deals with capital punishment (which I oppose), the general sentiment of punishment as a deterrence applies to any form of it.

So giving up on the idea of free will, rather than making crimes less punishable as people fear, actually makes it harder to escape punishment because it applies it more uniformly and consistently. “The devil (or god) made me do it” would not be a defense unless the perpetrator’s brain was such that he or she did not know the difference between right and wrong.

So what would we do with people who commit crimes but who, under the M’Naghten rule, are deemed to have a cognitive capacity that is so impaired that they cannot judge the difference between right and wrong and so the sole purpose of punishment, that of deterrence, will not work? “Even for those who are completely undeterrable, because of frontal-lobe damage, genes for psychopathy, or any other putative cause, we do not have to allow lawyers to loose them on the rest of us. We already have a mechanism for those likely to harm themselves or others but who do not respond to the carrots and sticks of the criminal justice system: involuntary civil commitment, in which we trade off some guarantees of civil liberties against the security of being protected from likely predators.” (Pinker, p. 185)

In the next post in this series, I will look at the broader implications for the lack of free will. But for the moment, the following clip has an interesting discussion involving cognitive scientists and lawyers on the implications of neuroscience and the new understanding of the lack of free will for the law (via Machines Like Us).


  1. says

    Good video clip…captures the complexities facing the legal system.

    It continues to suggest to me, that prisons, should become clinics (forced enrollment until rehabilitated). There is no reason to treat prisoners like warehoused non-humans.

    The key is determining when someone is rehabilited, but once so, release him. If someone can’t be rehabilited, he stays in the clinic.

    Clinic sentences are all the same….until rehabilitated.

    If the neuroimaging technology allows us to predict a predisposition for criminal activity, we treat the condition, just like we treat other medical conditions we predict will manifest detrimentally.

    The key obviously lies in the neurotechnology. We need to keep improving the technology….it seems to me there is a moral mandate.

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