Philosophy of Law Spring 2022

Compatibilism and Incompatibilism


It is generally believed that punishment presupposes responsibility. That is, it would be unjust to punish someone for doing something if he was not responsible for doing it. It’s assault if I bonk your head with mine on purpose. If I bonk your head because I trip, that’s an accident. It would be fair to punish me for assaulting you. But it would be unfair to punish me for an accident. I couldn’t help it, after all. That’s the idea.

So what does it take for me to be responsible for my actions? Another thing that is widely believed is that I can be responsible only for those things that I freely will to do.

OK, so what is a free will? You will not be surprised to hear that there are different schools of thought about this question.

One side believes that my will is free only if my decisions are not determined by causes I have no control over. The other side thinks that this makes no sense: how could anything not have a cause? They think that my actions are free only if I am not impeded from doing what I want to do and that this could be true even if what I do is determined by causes lying outside of my control.

This is the philosophical debate about free will. It strikes many people as a merely academic question. Since we will never know whether our actions are causally determined or not, we can’t apply it to real world institutions like the law. But the achievements in neuroscience have made the free will debate a more urgent matter. While we are not yet capable of showing exactly how decisions are caused, it seems quite possible that we will do so. That gives the free will debate a new kind of urgency.

For today’s class, I want to go over the basic positions on free will.

Compatibilism, Incompatibilism, and Libertarianism

There are two questions each of which has two answers: “yes” and “no”.

  1. Is determinism true? The two answers make up the columns in the table below.

  2. Is it possible that our actions are free and we are responsible for at least some of the things we do even if determinism is true? The answers here are the rows.

Determinism is true Determinism is false
Yes, freedom & responsibility are compatible with determinism Compatibilism (Morse) – (no one)
No, they aren’t (Incompatibilism) Hard Determinism (Greene and Cohen) Libertarianism (Libet)

These labels are wonky. “Incompatibilism” is the name of the bottom row but “compatibilism” is only the name of the northwest box. And “hard determinism” is the name for only the southwest box while plain “determinism” refers to the whole western column. But we play the hand we’re dealt. Here is what they mean.

Determinism is the view that everything that happens is causally determined. To put it another way, everything that happens is the effect of a separate cause and causes make their effects happen. This includes human actions.

Compatibilism is the view that our actions can be free, and we can be held responsible for what we do, even if determinism is true. Punishment is a way of holding people responsible for their actions.

Incompatibilism is the view that actions cannot be free, and we cannot be held responsible for what we do, if determinism is true.

Hard determinism combines incompatibilism and determinism.

  1. If determinism is true, actions cannot be free, and we cannot be held responsible for what we do. (Incompatibilist premise)
  2. Determinism is true. (Determinist premise)
  3. Therefore, our actions are not free and we cannot be held responsible for what we do. (Conclusion)

Libertarianism combines incompatibilism with the denial of determinism.

  1. If determinism is true, actions cannot be free, and we cannot be held responsible for what we do. (Incompatibilist premise)
  2. Determinism is not true because some things that happen are not causally determined. In particular, the decisions of the human will are not always causally determined. (Libertarian premise)
  3. Therefore, our actions can be free and we can be held responsible for what we do. (Conclusion)

How can you be a compatibilist?

Compatibilism is the more difficult position to understand, so I’m going to spend a little time going over it. I am going to take a fairly simple version of compatibilism derived from Thomas Hobbes, a seventeenth century philosopher and mathematician. There can be other versions that are more complicated, but this will do to get us started.

A person’s actions are free, according to this simple version of compatibilism, if she can do what she wants to do. The idea is that freedom means there is nothing external blocking you from doing what you want to do. It does not matter whether your decision to do one thing rather than another was caused by factors outside of your control.

Here is a boring example to illustrate this simple version of compatibilism. No one can control whether they are are thirsty; thirst is not a matter of will. But thirst is often the last appetite before action. It causes us to do things like getting a drink of water. Imagine the following dialog:

“Where are you going?”

“To the kitchen to get a drink.”


“Because I’m thirsty.”

That’s the most ordinary thing in the world. But no one really thinks that the fact that I have no control over whether I am thirsty means I am not free when I go to get a drink of water.

Yes, yes, you can decide not to go to the kitchen even if you are thirsty. Maybe sitting through class is more important to you than getting a drink right now. But a compatibilist is going to say the desire to sit through class is something else that you do not control. One way or the other, your decision is going to be caused by something outside of your control.

Compatibilists think that this kind of example shows that they are describing what we ordinarily call free actions. They concede that if you asked someone an abstract question about whether freedom is compatible with causal determination, that person would say no. But, they think, the ordinary person’s descriptions of concrete actions as free or unfree will match his definition. And the ordinary person’s abstract philosophical opinions are just confused: no one really understands what an uncaused action would be.

Two kinds of incompatibilism

Incompatibilism is the view that responsibility for our actions is incompatible with the causal determination of our actions. Incompatibilists split into two camps depending on whether they think our actions are caused or not.

Libertarians think that our actions are not caused. That’s why they deny that determinism is true. They think that there are some things in the universe that are not causally determined, namely, human actions. So they do not think that everything is causally determined.

Why would you be a libertarian? Perhaps you think that human beings are not exclusively material. If you think that a person has an immaterial soul and that this soul is what is responsible for making decisions, then you might think that our decisions are not subject to the laws that govern the physical universe. That is true of Bramhall, the author of the other optional reading. Benjamin Libet, a neuroscientist, is also a libertarian. He thinks that we have the ability to veto decisions made by our physical brains. We will encounter Libet when we read Morse; I also have an optional reading by him on Sakai.

The other branch of incompatibilism is called hard determinism. Hard determinists believe that our actions are caused and that causation is incompatible with responsibility. That is the view that Greene and Cohen will defend in the part of the article that we will read next time.

Consequentialism and Retributivism

Compatibilists are usually consequentialists about punishment. Incompatibilists, by contrast, are usually retributivists.

Compatibilists think our behavior is caused, so they tend to look for causes of good behavior, like deterrent threats.

Incompatibilists think that we are responsible for our actions only if we are free from causal influence. They think responsibility for actions has to be attached solely to the person who acts. So it is natural for them to think that the point of punishment is retribution for freely chosen evil.

That said there is no logical reason why the views on free will have to line up with those views about punishment. As we will see next time, Greene and Cohen are consequentialists about punishment but incompatibilists about responsibility.

Main points

You should be familiar with these points from today’s class.

  1. Compatibilism.
  2. Incompatibilism.
  3. Relationship with consequentialist and retributivist theories of punishment.


Greene, Joshua, and Jonathan Cohen. 2004. “For the Law, Neuroscience Changes Nothing and Everything.” Philosophical Transactions of the Royal Society 359 (1451): 1775–85.