I’ve been reading a lot of early modern philosophy recently, so here are a few different perspectives on free will from that era. Descartes was a libertarian, Spinoza was a hard determinist, and Hume was a compatibilist.
Descartes was, famously, a substance dualist, which meant that he thought that the mind was actually an immaterial thing distinct from the brain. He thought that it was self evident that we have libertarian free will, conceived as the ability to affirm, deny or suspend judgment about a proposition that has been put before us and as the ability to choose what actions we perform. Descartes also thought that all of the actions that occur in the physical world are completely determined by the mechanistic laws of physics, which made it difficult to explain how the mind, which was immaterial and non-deterministic, could interact with and effect change upon the body, which was material and deterministic. His “solution” was that the soul exerts control over the body through the pineal gland, which is hardly a solution.
Spinoza was a little more consistent than Descartes. He was a panpsychist, meaning that he thought that everything physical was conscious in some degree. He actually thought that everything physical was identical to a conscious state, conceived under a different aspect. My mind and my body are just different ways of looking at the same thing, on this view. The body is governed by the laws of physics, which Spinoza claims reduce to a few self evident principles that we know a priori (he lays these out in the Ethics, and yes, they are all wrong), and the mind is governed by a different set of principles that always have the same results as the laws of physics. So for example, my belief that I am wearing a green shirt is identical to some physical state of my body, and my body is acting according to the laws of physics, and my mind is acting according to the laws governing states of consciousness, but both the laws of physics and the laws governing consciousness have the same result, namely that I currently have this belief.
Spinoza is not a substance dualist, because he thinks that the mind reduces to a bunch of different beliefs and desires that don’t have a common underlying substratum. There is no “self,” for Spinoza, just a bunch of different mental states. Further, Spinoza thinks that everything that happens is absolutely necessary, like it is necessary that 1+1=2. So, there is no question of our having free will, in Spinoza’s view, because there is no one to exercise the free will and even if there was, their decisions would be completely determined by the laws of physics and logic. The appearance that we have free will is an illusion created by our ignorance of our own mental processes.
This raises a problem for Spinoza that I mentioned in a previous post. Namely, if there is no self and everything we do is determined by the laws of physics, why should we trust any of the conclusions that we arrive at? Spinoza would address this concern, I think, by dissolving the distinction between truth and justification. He says at one point that “truth is its own criterion.” Spinoza thinks that if one of your beliefs is true, as opposed to arrived at by accident, then you have proved it by such a powerful a priori deductive argument that there is no way you can be wrong. So, the issue of justification doesn’t really come up for Spinoza, because there is no way of questioning the conclusion of an overwhelmingly powerful deductive argument like he requires for knowledge (although one might wonder whether we ever have knowledge that is this powerfully justified).
Hume’s conception of free will is based on his moral psychology. For Hume, as for Spinoza, the mind is a succession of beliefs and desires rather than a single, unitary entity. According to Hume, we act when a belief aligns with a desire. For example, I perform the action of going to the store because I want ice cream and I believe that there is ice cream at the store. This is a deterministic account of action, but Hume doesn’t see it as opposed to free will. Instead, he argues that free will consists in “liberty of spontaneity,” the ability to act without being coerced by an external force. Hume thinks that liberty of spontaneity is not only the only kind of free will we could possibly have, but also the only kind of free will that is consistent with the institution of moral responsibility.
I view my position on free will as distinct from any of these. I am a libertarian, like Descartes, and I agree with Descartes that libertarian free will is self evident, but unlike Descartes, I don’t view consciousness or free will as supernatural. Free will is not a puzzle to be explained by means of mysticism, but rather a normal part of the natural world that can in principle be studied and understood by science.