Philosophy of Law Spring 2022

Modern Compatibilism


Morse’s article tries to answer two challenges from neuroscience. The first challenge is that neuroscience seems to show that the brain causes behavior. The second challenge is that neuroscience seems to show that mental states like beliefs, desires, and intentions do not cause behavior.

The first challenge maintains that the brain does cause behavior.

  1. Punishment is justified only if the person who is punished was the cause of the behavior in question.
  2. If the brain causes behavior, then the person does not.
  3. Neuroscience will show that all behavior is caused by the brain.
  4. Therefore, neuroscience will show that punishment is never justified.

The second challenge maintains that beliefs do not cause behavior. I will calls this the “threat to folk psychology” below.

  1. Punishment is justified only if those who are punished are rational.
  2. People are rational only if (a) they can have accurate beliefs about the law and their behavior and (b) they are capable of acting on those beliefs.
  3. Neuroscience will show that beliefs play no role in causing behavior.
  4. Therefore, neuroscience will show that punishment is never justified.

Morse is especially worried about the second challenge because it threatens to undermine the legal standard for responsibility. The legal standard is rationality: people are liable to punishment only if they are rational. Rationality involves acting on one’s beliefs and desires: rational people act in ways that they believe will enable them to get what they want. If beliefs and desires do not cause actions, then rationality is irrelevant to how we behave and the legal standard of rationality is misconceived.

The Law’s Compatibilism

The law recognizes excuses for behavior that violates the criminal law. People who do not meet the standards of rationality cannot be punished for their actions.

So what does it mean to be rational? The main component, according to Morse, concerns knowledge: rational people understand what the law requires and the nature of their own behavior (Morse 2010, 842).

Note that this is a pretty low bar. You can do something that you know to be stupid and still count as rational as far as the law is concerned. You just have to be capable of understanding what the law requires and what you are doing.

The law also recognizes external compulsion or coercion as excuses. Those who break the law with a gun to their heads are excused even though they do not suffer from defects in their rationality.

This raises a question about what is sometimes called “internal” compulsion. Cases of internal compulsion involve people who cannot control their behavior. They do what they know to be wrong for reasons that, they maintain, are out of their control. Is internal compulsion an excuse and, if so, why? Morse treats these cases as defects of rationality (Morse 2010, 843). His presentation of his opinion here is quite terse, so I am not entirely confident that I have him right. The idea seems to be that cases of internal compulsion involve an inability to control one’s behavior in the light of what one knows to be right. So you can know what the law is and what your behavior involves but still suffer from a lack of rationality if you can’t bring your knowledge to bear on your actions. The idea is that these cases are similar to cases of external compulsion because it is unusually difficult for the person to make the correct choice. Consequently, the law excuses the behavior in both kinds of case.

(I had a remark here about how it’s rational to comply when you have a gun to your head, but I removed it because it was a mistake; Morse did not say otherwise.)

In any event, we know that the law excuses people who are subject to external and internal compulsion. The important thing for Morse is that the legal excuse cannot be generalized from these specific causes of behavior to all causes of behavior. So, he maintains, you can be excused if you were forced by a gun to your head but not if your behavior was the product of causal forces that originated with the big bang.

We will talk more about internal compulsion next time, when we discuss the unfortunate Kevin.

The Threat to Folk Psychology

What really worries Morse is the possibility that neuroscience will displace what he calls “folk psychology.” When we employ folk psychology, we explain people’s behavior as the product of their beliefs, desires, and intentions. Morse believes the law assumes folk psychology is accurate and that beliefs, desires, and intentions really do explain why people do the things they do.

Suppose we ask whether someone’s behavior is rational or not. One way of answering that is to see whether it reflects the person’s beliefs and desires or not. Your behavior is rational if it makes sense in the light of what you want to achieve and your beliefs about how to achieve it. If you want to go to lunch and you believe that the cafeteria is to the west of here, your behavior of walking west towards the cafeteria is rational. If you walk south despite believing there is no place to eat to the south, your behavior is irrational.

Here is Morse’s nightmare. If neuroscience displaces folk psychology one of the assumptions the law relies on would have been shown to be false: the assumption that our behavior can be rational. If your beliefs and desires don’t actually govern your behavior, then the way we assess rationality will be divorced from the behavior we want to evaluate.

The evidence that Morse describes comes from experiments done by Benjamin Libet (Libet 1999). These seem to show that the brain starts acting before the person is consciously aware of having decided to act. That suggests that the intention to act is not the cause of our actions: it happens after the brain takes the first steps to cause an action.1

Main Points

Here is what you should know or have an opinion about from today’s class.

  1. How Morse answers the charge that the brain causes behavior.
  2. The rationality standard for punishment.
  3. Morse’s worry about the second charge, that “folk psychology” is not true.

Folk physics at work

Morse’s worry is that folk psychology is going to go the way of folk physics, that is, the explanations of physical phenomena that are good enough for everyday life but actually false.

To illustrate folk physics, you can do a little experiment. Pick up a heavy book in one hand and a piece of paper in the other hand. Now ask yourself this question. “If I were to drop both at the same time, which one do I believe will fall the fastest?”

If you are honest, your answer is going to be “the heavy book.”

If you figured that I was asking a trick question, you might say “um, they will fall at the same rate?”

That’s the correct answer. But none of us believe it. That’s folk physics in action. We all think the heavier object falls faster. It’s nearly hard wired in our heads even though it is not true.

You still don’t really believe it. I know this because you are going to be genuinely surprised when you see what happens when you drop a bowling ball and a feather in a vacuum.

Was I right? Were you amazed? If not, you are made of sterner stuff than I am.

This is the what Morse is thinking. Folk physics is false. Even though we believe it as we go about our daily lives, engineers and physicists know not to use in when they are making important things like bridges and airplanes. If neuroscience shows that folk psychology is false like folk physics is, maybe lawyers and judges shouldn’t use it when they are making important decisions about guilt and innocence.


Libet, Benjamin. 1999. “Do We Have Free Will?” Journal of Consciousness Studies 6 (8–9): 47–57.
Morse, Stephen J. 2010. “Scientific Challenges to Criminal Responsibility.” In Philosophy of Law, edited by Joel Feinberg, Jules Coleman, and Christopher Kutz, 9th ed., 839–53. Belmont, CA: Wadsworth.

  1. Libet himself has a libertarian view of free will on the grounds that neuroscience has shown that we have an unexplained ability to intervene in the causal chain between the brain’s activating to move the finger and the finger’s actually moving (see Libet 1999, 51–53). I put the Libet article on the sakai site; it’s optional, but people are usually interested.↩︎