Kevin and the Insanity Defense

We talked about the case of “Kevin” as presented by Radiolab.

Necessary conditions on responsibility

What are the necessary conditions for being responsible for your actions, where “being responsible” means that you could be justifiably punished for what you did?

Incompatibilists say the necessary condition is that you have to be the cause of your behavior, free from any other causes outside of your control.

The law, as represented by Morse, maintains that the necessary condition is rationality: you can be responsible for your behavior only if you were rational when you did it. In this way, the law is compatibilist: it holds that rationality is the only necessary condition for being responsible for your behavior. So even if your behavior is caused, you can be responsible for it so long as you were rational when you did it.

We started off today’s class with two more detailed statements of what rationality involves. These come from attempts to devise criteria for determining when insanity is an appropriate defense against a criminal charge.

  1. Knowledge of (a) right and wrong and (b) what you are doing. This is the M’Naghten Rule.
  2. Knowledge and control of your behavior in the light of what you know. This is the position of the American Law Institute.

If we use the M’Naghten Rule, Kevin is pretty clearly responsible.

If we use the American Law Institute standard, it’s at least debatable whether he is responsible or not. On the one hand, there is a lot of evidence that his behavior was something that he could not control. On the other hand, there is some pretty good evidence that he had some control and there is at least a suggestion that he could have known to get help to exert even greater control.

The big picture

If we’re going to say that Kevin should not be punished because his brain was responsible rather than him, then we are on the road to saying that no one can be punished. After all, everyone’s brain is responsible for their behavior. At least, that’s what materialistic neuroscience seems to be on the road to showing … someday.

It was notable to me that few of the people in the story said something like that. Kevin, his wife, the judge, and the prosecutor all applied the compatibilist standards of rationality. They were primarily interested in whether he was capable of controlling his behavior in the light of his knowledge of right and wrong, which is the American Law Institute standard for rationality.

Everyone agrees on the facts of the case. What is at issue is how we understand or interpret them. That is where philosophy comes in. If we interpret the story of Kevin as showing that punishment is inappropriate because his actions were caused by his brain, we are headed towards incompatibilism. If we interpret the story as showing that the law’s normal standards for assessing rationality and insanity can be applied to a case like this, then we are taking up a compatibilist position.

Matthew, who cannot be put in a box, pointed out that we had neglected one possibility. You could be a dualist libertarian who thinks that the brain can interfere with your freedom. That is, you could think the following things:

  1. A person is distinct from the brain and so
  2. it is possible for a person’s actions to be free from causal determination
  3. but damage to the brain could interfere with a person’s ability to act freely.

Of course, there are a lot of details to be filled in. But the point is a good one. We have seen sophisticated versions of compatibilism (Hobbes, Morse, and the two proposed standards for insanity) and we have seen a sophisticated version of hard determinism (Greene and Cohen), but we have not seen a version of libertarianism more sophisticated than Bramhall’s. And while Bramhall does score some points, he is not as skilled at this sort of thing as some of the others. We should not take the gap in our readings as meaning that this position could not be filled.

Key concepts

  1. The facts of Kevin’s case
  2. The difference between the M’Naghten Rule and the American Law Institute’s rules
  3. Do you interpret Kevin’s case in an incompatibilist way or a compatibilist one? That is, do you think he should not be blamed because his brain injuries are responsible for his behavior or do you think the law’s normal standards can be appropriately applied to his case?


Oliver Sacks wrote up a description of what appears to be the same case, just in case you would like to read more.


American Law Institute. 2010. “The Insanity Defense.” In Philosophy of Law, edited by Joel Feinberg, Jules Coleman, and Christopher Kutz, 9th ed., 836–39. Belmont, CA: Wadsworth.

House of Lords. 2010. “The M’Naghten Rules.” In Philosophy of Law, edited by Joel Feinberg, Jules Coleman, and Christopher Kutz, 9th ed., 835–36. Belmont, CA: Wadsworth.