A person on the internet argued that we don't have free will since our choices are determined by our desires, we don't choose our desires, and we couldn't have done otherwise. In my response, I avoided terms like "libertarianism" and "compatibilism," but that's what I was talking about. I basically gave a short defense of the compatibilist notion of free will against the libertarian notion of free will. Here's what I said:
If it's true that our desires determine our choices, then isn't it the case that we could have done otherwise if we had wanted to? Does the ability to do otherwise have to be categorical, or can't it be qualified?
It seems to me that if my actions arise out of my own desires, then I am doing exactly what I want to be doing, and if I'm doing exactly what I want to be doing (as opposed to being forced or determined to act contrary to my desires), then I am acting freely.
Consider the alternative. Imagine that my every desire is to choose X, but somehow, spontaneously, I end up choosing not-X. It seems to me that if my choice of not-X isn't preceded by my desire, then I couldn't have done it on purpose. And if I didn't do it on purpose, then it was not in my control. And that means I was forced, by this spontaneous event, to act contrary to my desire. Why call that freedom at all? It seems to me that's a denial of freedom.
So we can only be free to the degree that we control our own actions, and we can only control our own actions to the degree that our actions are determined by our antecedent desires. That means we are most free when our actions are determined by our desires.
That's free will in the most meaningful and useful sense because it leaves us in control of our own actions, and it leaves room for moral culpability. It also keeps the world from being random and chaotic.
I don't see why it should matter that we don't choose our desires. The supposition that we'd have to choose our desires results in an infinite regress. Before I could do anything, I'd first have to have a desire. But before I could have that desire, I'd first have to choose it. But before I could choose it, I'd first have to want to. Before I could want to, I'd first have to decide to want to. Etc. etc.
There's one of two ways to avoid this infinite regress. You can either start with a choice that is not determined by any desire, or you can start with a desire that is not the result of your choice. We've already seen that if you have a "choice" that happens apart from any antecedent desire, then it's not really a choice at all since you couldn't have intended to do it. It was an accident that was random, and you had no control over it.
So the only alternative is that our choices originate in desires that we did not choose. That's the only way we can have any meaningful kind of freedom because it's the only way we can do anything on purpose.
For further reading on this subject, check out my series on "William Lane Craig against Calvinist," especially Part 3B and Part 4.
