Now is the time when we look back over the past year and wonder: how did I do? Did I make the right decisions? Could I have made better ones?

Well, could you? A determinist who believes that the world unfolds in an inexorably preordained manner would say not. If, on the other hand, you believe in free will, you might feel sure that other decisions were available to you, other paths not taken. “I could have done otherwise” is sometimes taken as the very definition of free will.

But asking if you could have chosen differently is not a yes or no question – in fact, it is simply devoid of meaning. If free will exists, it’s not to be found by asking whether we could have chosen differently.

Sure, that sounds odd. But if we want to talk about actual physical reality, such hypotheticals are irrelevant. Think about it. If you’re wondering whether you should have bought that other car, what does that really mean? You pondered it for days, all of that cogitation feeding into your decision. A whole bunch of other stuff, working out of conscious sight, was influencing your choice too – even, perhaps, what you had for breakfast. (A study in 2011 found that judicial rulings are systematically more lenient after the judges’ lunch break.) What exactly do you imagine changing, then, in this world where you chose differently? Where do you stop? There is no such world in which “everything is the same except my decision”. The decision is not somehow superimposed on the rest of the world, but emerges from it.

It’s the same if we ask about changing the future. A determinist will deny that you can do this – what is going to happen is preordained. But that doesn’t mean they can tell you what that future will be, even if they can make some pretty good predictions about aspects of it. This isn’t just a question of their having incomplete information; we’ll always lack information. Rather, a completely accurate prediction requires your predictive model to omit essentially nothing – to be indistinguishable from the world itself (so-called computational irreducibility). Add that to the sheer randomness of events at the quantum level and you see that it is impossible to be totally sure of anything that happens until it happens. We can only know the future when it arrives.

In other words, the future too is something that cannot be changed – not because the world is deterministic and we lack free will, but by definition: the future is simply “what happens”. A determinist who says at every instant: “That was bound to happen, though I couldn’t have predicted it” is not adding anything to this simple fact.

Yet still we ask both whether we could have acted differently in the past and whether we can change the future. When we do that, however, we’re not wondering about things that truly happened or might happen; we are deploying the imaginative capabilities of our minds. That’s the extraordinary thing about the mind: it is unbounded. As Emily Dickinson wrote: “The Brain – is wider than the sky.” We are constantly creating alternative mental worlds based on our internal models of how the real world works. They may or may not correspond to what happens or what happened, and they’ll certainly ignore almost everything that does happen. They are, in other words, part of the cognitive apparatus of decision-making itself. As philosopher Daniel Dennett says, the mind “mines the present for clues … turning them into anticipations of the future”. That is, in a sense, what minds are for.

Could these imagined worlds have come to pass, or occur in the future? The answer is not yes or no; asking the question is itself the point, for it motivates behavioural choices. In other words, we are asking about the neurobiology of volition – which should be the real locus of discussions both about “free will” and moral responsibility. As cognitive scientist Anil Seth says, the point of having what we call free will is not so that we do anything differently in the moment (different from what?), but that we can learn from our actions to reset our volitional circuitry and make better choices in the future.

This is really why we ask: “Could I have done otherwise?” As Dennett says: “We ask it because something has happened that we wish to interpret … That is, we want to know what conclusions to draw from it about the future.” The main thing, says Dennett, “is to see to it that I will jolly well do otherwise in similar situations in the future” (if indeed it’s something we regret). But do we have that self-determining power, or are we just automata driven by forces beyond our ken or control? Contrary to what is often claimed, modern science does not insist that you are at the whim of your particles. (And don’t be misled by those famous neuroscientific experiments allegedly showing our actions are predictable from brain activity before we’re conscious of having made the decision; they are a red herring.) Instead, it seems to show that, in complex systems like the brain, causal power doesn’t all flow from the bottom up. Our volitional neural circuits are genuine causes of things that happen. We don’t change the future (a meaningless concept), but rather we are a part of what creates it.

That, as Dennett says, is the basis of “free will worth wanting”. I think even some determinists know this deep down. The claim in physicist Sabine Hossenfelder’s book Existential Physics that “the future is fixed except for occasional quantum events that we cannot influence” is rather undermined by her remark that “progress [in science] depends on choice and effort. It is up to us.” Thankfully, it is.

The mental leap to this perspective is both empowering and liberating. To think: “If only I’d chosen X, not Y!” could be a rod for your own back – a source of regret and self-flagellation. Or it could be a learning opportunity: “Now I know what I’ll do next time.” Perhaps this year you will.

• Philip Ball is a science writer and the author of The Book of Minds: How to Understand Ourselves and Other Beings, from Animals to Aliens (Picador, £16.99). To support the Guardian and Observer, order your copy at guardianbookshop.com. Delivery charges may apply.

Further reading

Elbow Room by Daniel C Dennett (MIT Press, £20)

Making Sense of Freedom and Responsibility by Dana Kay Nelkin (Oxford University Press, £31.99)

Being You by Anil Seth (Faber, £9.99)