This is the the thirty-eighth post in my Theories of Knowledge and Reality series. Follow the link for more on the series and for links to other entries as they appear. In the last post, I defined 'determinism' and distinguished it from a view that is sometimes called fatalism. In this post I'll look at some positive arguments for thinking determinism is true and some positive arguments for thinking we are free.
Keep in mind the definition of determinism: "given the laws of nature and the state of the universe at any one time, there is only one possible state of the universe at any later time." Why might someone think this is true? I can think of two sorts of reasons why someone might think something like this. One is theological, and the other is scientific.
Some people who believe in God think of God as the sort of being who has absolute control over all of creation. Those who take such a strong view of God's sovereignty will often end up saying things very much like what determinists say. Depending on the details of the view, it may or may not be technically the same thing as determinism. To be determinism, God's means of controlling every event would have to be by setting up the laws of nature in a way that they guarantee every outcome God desires. If the laws of nature are not deterministic in that way, and God just constantly intervenes in the natural order, then it isn't strictly speaking determinism as I've defined it. But it's a sort of theological determinism, with God's interventions causing everything in a way similar to how laws-of-nature determinism would.
One thing to keep in mind about this reason for holding determinism (or really something near enough to determinism) is that it's not really an argument. It's a motivation based on other views. Perhaps there are good arguments for those other views, but it won't convince people who don't hold those other views. Since these views include the controversial claim that God even exists, that limits its force right there, and many theists do not hold such a strong view of God's sovereignty. So this isn't going to motivate everyone to believe something like determinism.
The scientific motivation for determinism is much stronger. In science, we explain things. We seek to explain events in terms of what caused them to happen. We assume that something wouldn't happen unless something caused it to happen. Otherwise why bother to find such explanations for everything that takes place? Now it's possible that most events have such explanations, and a few events do not. But a simpler explanation that treats nature as uniform would not expect such vastly different characteristics of events. If we can make sense of reality with a coherent explanation that applies to everything, we should do so. So the question is really whether there are good reasons to believe of any particular events that they are uncaused.
It turns out that there is scientific evidence for thinking some events are uncaused. In quantum mechanics, some puzzling equations lead a number of scientists to this conclusion. Technically speaking, there are several interpretations of the import of those equations. A philosopher of physics who has published work on the subject once told me that he doesn't think any of the interpretations are actually consistent with the equations, but they're the best we have at the moment. That leads me to want to take what follows with a grain of salt. But it does seem that the dominant interpretation of the equations is that some events on the tiniest level of reality we know about are not caused. That is, right now there is nothing about the world at that micro-level that, given the laws of nature, determines how things at that micro-level will be in the future.
But even if you accept this dominant interpretation at the micro-level, there are differences of opinion in the philosophy of physics about what that means for the macro-level that we can directly observe. Another philosopher of physics I know thinks the micro-level indeterminism is perfectly consistent with macro-level determinism. That is, however these micro-indeterminacies work themselves out, the same result will happen at the macro-level. Since these discussions are all extremely technical, I'm simply taking the word of philosophers of physics I know and respect, but it seems to me that it isn't clear at all that quantum mechanical observations have shown determinism to be false in any way that it matters. Perhaps they have undermined some of the motivation for determinism, but I don't take any of this to be rock-solid proof one way or the other. It will also be clear as the series goes on that those who think determinism is incompatible with freedom don't end up getting much help from indeterminism at the quantum level either, but I'll save that argument for a future post.
What should we conclude from all this? Well, there is a strong argument from scientific practice for determinism, one that is somewhat undermined but not necessarily in any helpful way by quantum mechanics. There is a strong argument from quantum theory that indeterminism is true at the micro-level, but it's also not clear that such indeterminism will make a difference in terms of what we regularly experience at the macro-level. In the end, I don't think we should place much stock in the scientific arguments. Determinism may or may not be true, as far as science shows us, and science has changed enough that current science may not be exactly right anyway. If we come to understand things at a deeper level than quantum mechanics, who knows where things will go? In the end, I don't take these arguments to be all that strong. That leaves me open to either determinism or indeterminism, and we're left looking at what follows from either view without being sure which is true.
In the next post, I'll look at some positive arguments for thinking we are free.