One reason that modern-day debates between atheists and religious believers are so bad-tempered, tedious and infuriating is that neither side invests much effort in figuring out what the other actually means when they use the word 'God'. This is an embarrassing oversight, especially for the atheist side (on which my sympathies generally lie). After all, scientific rationalists are supposed to care deeply about evidence. So you might imagine they'd want to be sure that the God they're denying is the one in which most believers really believe. No 'case against God', however watertight, means much if it's directed at the wrong target.

Yet prominent atheists display an almost aggressive lack of curiosity when it comes to the facts about belief. In The God Delusion, Richard Dawkins expertly demolishes what he calls 'the God hypothesis', but devotes only a few sketchy anecdotes to establishing that this God hypothesis is the one that has defined religious belief through history, or defines it around the world today. AC Grayling insists that atheists are excused the bother of actually reading theology – where they might catch up on debates among believers about what they believe – because atheism "rejects the premise" of theology. And when The Atlantic ran a piece last year entitled Study theology, even if you don't believe in God, Jerry Coyne, the atheist blogosphere's Victor Meldrew, called it "the world's worst advice." And on and on it goes.

My modest New Year's wish for 2014, then, is that atheists who care about honest argument – and about maybe actually getting somewhere in these otherwise mind-numbingly circular debates – might consider reading just one book by a theologian, David Bentley Hart's The Experience of God, published recently by Yale University Press. Not because I think they'll be completely convinced by it. (I'm not, and I'm certainly not convinced by Hart's other publicly expressed views, which tend towards the implacably socially conservative.) They should read it because Hart marshals powerful historical evidence and philosophical argument to suggest that atheists – if they want to attack the opposition's strongest case – badly need to up their game.

The God attacked by most modern atheists, Hart argues, is a sort of superhero, a "cosmic craftsman" – the technical term is "demiurge" – whose defining quality is that he's by far the most powerful being in the universe, or perhaps outside the universe (though it's never quite clear what that might mean). The superhero God can do anything he likes to the universe, including creating it to begin with. Demolishing this God is pretty straightforward: all you need to do is point to the lack of scientific evidence for his existence, and the fact that we don't need to postulate him in order to explain how the universe works.

Some people really do believe in this version of God: supporters of 'intelligent design', for example – for whom Hart reserves plenty of scorn – and other contemporary Christian and Muslim fundamentalists, too. But throughout the history of monotheism, Hart insists, a very different version of God has prevailed. In a post at The Week, Damon Linker sums up this second version better than I can:

… according to the classical metaphysical traditions of both the East and West, God is the unconditioned cause of reality – of absolutely everything that is – from the beginning to the end of time. Understood in this way, one can’t even say that God "exists" in the sense that my car or Mount Everest or electrons exist. God is what grounds the existence of every contingent thing, making it possible, sustaining it through time, unifying it, giving it actuality. God is the condition of the possibility of anything existing at all.

God, in short, isn't one very impressive thing among many things that might or might not exist; "not just some especially resplendent object among all the objects illuminated by the light of being," as Hart puts it. Rather, God is "the light of being itself", the answer to the question of why there's existence to begin with. In other words, that wisecrack about how atheists merely believe in one less god than theists do, though it makes a funny line in a Tim Minchin song, is just a category error. Monotheism's God isn't like one of the Greek gods, except that he happens to have no god friends. It's an utterly different kind of concept.

Since I can hear atheist eyeballs rolling backwards in their sockets with scorn, it's worth saying again: the point isn't that Hart's right. It's that he's making a case that's usually never addressed by atheists at all. If you think this God-as-the-condition-of-existence argument is rubbish, you need to say why. And unlike for the superhero version, scientific evidence won't clinch the deal. The question isn't a scientific one, about which things exist. It's a philosophical one, about what existence is and on what it depends.

But too often, instead of being grappled with, this argument gets dismissed as irrelevant. Sure, critics argue, it might be intriguing, but only a handful of smartypants intellectual religious people take it seriously. The vast majority of ordinary folk believe in the other sort of God.

As Hart points out, there are two problems with this dismissal. First, you'd actually need to prove the point with survey data about what people believe. But second, even if you could show that most believers believe in a superhero God, would that mean it's the only kind with which atheists need engage? If a committed creationist wrote a book called The Evolution Delusion, but only attacked the general public's understanding of evolution, we'd naturally dismiss them as disingenuous. We'd demand, instead, that they seek out what the best and most acclaimed minds in the field had concluded about evolution, then try dismantling that.

Which is also why atheists should read Hart's book: to deny themselves the lazy option of sticking to easy targets. Perhaps you'll come away convinced. But even if all you do is clearly articulate why you think he's completely wrong, you'll be helping to lift the discussion far above what usually passes for debates about religion.