There is an important argument that many find makes a compelling case for Incompatibilism.
Some texts call this the Consequence Argument; others call it the Before You Were Born Argument.
The argument goes as follows:
If Determinism is true, then how we act today and in the future is the necessary consequence of the laws of nature and the way the world was before we were born. But it is not up to us what went on before we were born. And neither is it up to us what the laws of nature are. We have no control over those things. And if it’s not up to us whether certain things happen, then neither is it up to us whether the consequences of those things happen. If we have no control over the laws and the past, and they have the inevitable physical consequence that we will act a certain way, then we have no control over how we act. Hence, if Determinism is true, then it is not up to us how we act today or in the future.
This is called “the Consequence Argument,” because it appeals to the principle “If we have no control over certain things, then we don’t have control over the consequences of those things, either.”
Lemos presents the Consequence Argument on pp. 24–5.
van Inwagen presents the argument starting on the bottom of p. 273 and ending 2/3 of the way down p. 276. The claim I’ve highlighted in purple correspends to what he calls “the Principle.”
Where I've said that something is "not up to us," van Inwagen says that it's "untouchable," meaning that you are and always were unable to do anything to alter it (and couldn't have done anything even if you knew more or were more lucky).The Consequence Argument makes a very strong case for the conclusion that Determinism will be incompatible with free will. There are things a Compatibilist can say in response, but those things are rather subtle and may not be convincing.
Here is a development of the Compatibilist ideas that Beebee will be suggesting.
Philosophers distinguish a number of different senses of “possibility.” One kind of possibility is “physical possibility.” We say that some event is physically possible (with no qualifications) iff it’s compatible with our laws of nature that that event take place. We can say that an event is physically possible at time t iff it’s compatible with our laws of nature, and the actual state of the universe at t, that the universe evolve in such a way from t so that that event comes about. (van Inwagen describes such a distinction on pp. 271–2 of his reading. He expresses the second as “having a physically possible connection with time t.”)
Another kind of possibility philosophers discuss is “epistemic possibility.” Roughly, something is epistemically possible iff it might be true, for all we know.
Now, we also employ claims like “It’s possible for me to do A” when we’re talking about what it’s in our power to do. Say that an act A is volitionally possible for me at time t iff, at t, it’s in my power to do A. If doing A and refraining from doing A are both volitionally possible for me at t, then it is up to me at t whether to do A. (We may want to subdivide the notion of volitional possibility further, since as we’ll discuss in upcoming classes, what we mean by “in my power” is sometimes different.)
The relations between these different kinds of possibility are not very straightforward. An important issue in recent philosophy is that some things may be imaginable or conceivable, and so epistemically possible in some sense, even though they’re not possible in other ways, including being physically possible. So “it is epistemically possible that P” will not entail “it is physically possible that P.”
The Incompatibilist assumes that, if doing A is in your power right now, then it must be compatible with the laws of nature, and the present state of the universe, that you do A. That is, he assumes that: “It is volitionally possible for you at t to do A” does entail “It is physically possible at t that you do A.”
However, the Compatibilist thinks that the mere fact that you’re causally determined not to do A does not by itself settle the question whether you could do A. The Compatibilist thinks that, even if your doing A is ruled out by the laws of nature and the present state of the universe being as they are, doing A might nonetheless be something which is in your power. That is, according to the Compatibilist: “It is volitionally possible for you at t to do A” does not entail “It is physically possible at t that you do A.” Some things can be volitionally possible at t which are not physically possible at t.
Why would anyone believe this? How could it be in your power to violate the laws of nature, or to make the past be other than the way it is?
Well, forget about Determinism for a moment. Think about an oracle 500 years ago who could look in her crystal ball, and see everything you’re now going to do. This is controversial, but many philosophers will agree that it’s already being true that you won’t do A doesn’t, by itself, entail that you are unable to do A. The fact that you won’t do it doesn’t show that you can’t do it. Similarly, the fact that the oracle has already seen that you don’t do it does not show that you can’t do it. It only shows that, as a matter of fact, you won’t do it.
Now here you are, deciding whether or not to do A. We suppose that you could do A. What does that show about your relation to the oracle? If you had done A, then presumable the oracle would have seen you doing A, instead of what she actually sees. Does that mean that your doing A today would have caused the oracle to see something different, 500 years ago? That sounds strange. How can what you do now cause something different to happen 500 years in the past? Some philosophers will say that, if the oracle really saw you do it, and wasn’t just guessing, then yes, you’ll have needed to cause her vision in the past. But another thing we can say is this. You have the power to do A, and if you had done A, and the oracle had retained her fortune-telling powers, then she would have seen you doing A. This is not the same as your having the power to cause or make the oracle see anything.
Regardless of whether you think any such fortune-telling oracles are possible, this is a helpful distinction to make when we’re thinking about free will and the Consequence Argument.
Could you have prevented the laws of nature and the past from being as they are? The Compatibilist will say: there’s nothing you can do which would cause the laws and the past to be different. Just as there’s nothing you can do now to cause the oracle to see something different 500 years ago. But that doesn’t settle the question we’re interested in. There may be things you can do (but won’t do), such that, if you were to do them, the laws and the past would have been different. In the same way that there may be something you can do (but won’t do), such that if you had done it, and the oracle had retained her powers, she would have seen something different in her crystal ball.
That is the core move in the Compatibilist’s response to the Consequence Argument. According to the Compatibilist, there are things you can do, even though the laws and the past have the consequence that you don’t do those things. The Compatibilist accepts that you can’t make the laws and the past be different. It’s just that there are certain things you can make happen, such that, in a counterfactual situation where you do make those things happen, the laws and the past would have been different. (For example, they may have been different in such a way that they guaranteed that you would do those things.)
That is how the Compatibilist will argue that things can be volitionally possible for you, or in your power to do, even though it is not now physically possible for you to do those things.
As I said, it is a subtle response to the Consequence Argument. Personally, I do think it’s an effective response; but not everyone finds it convincing. Some philosophers feel that it’s a kind of “trick.” I don’t think it is a trick. But it would take a lot more discussion to settle that.