The evidential argument from evil can be presented as follows:

An evil, in this context, is either a natural or a moral evil. Moral evils are the morally bad things that we do as free moral agents (we start wars, steal, murder each other, and so on). Natural evils are the natural diseases and disasters that cause suffering.

A gratuitous evil, in this context, is an evil that God lacks an adequate reason to allow.

Note that this version of the evidential argument from evil is a valid deductive argument: necessarily, if the premises are true, then so is the conclusion. The second premise looks very plausible. Perhaps God – by which we mean a being that is all-powerful, all-knowing, and all-good – will allow some evils if that's required for certain greater goods. But will God allow gratuitous evils – evils he has no adequate reason to allow? Presumably not. An omnipotent and supremely benevolent deity won't allow pointless, unjustified suffering, for example. And yet the world is filled not just with a great deal of evil, but also what appears to be a great deal of gratuitous evil. Hundreds of millions of years of animal suffering, for example, seems unjustified from a divine perspective. For couldn't God easily have created the world with us in it but without such a horrific past?

Is this a good argument against the existence of God?

Theists have responded in a variety of ways. One is to construct theodicies. A theodicy attempts to come up with a plausible God-justifying reason for the evil, thereby showing that the evil is not a gratuitous after all.

So, for example, some theists attempt to explain the pain and other suffering we endure:

1. (i) as a product of the workings of the laws of nature that are, on balance, good (those laws allow for great goods, such as our ability to interact causally with each other, but have downsides, such as producing earthquakes),

2. (ii) as a product of our own free actions. God set us free to do good of our own volition, and thus do moral good. The price God has to pay to allow this very great good is that this same freedom also allows us to do evil: to start wars, harm each other, and so on.

3. (iii) as offering character-building and other opportunities otherwise not available to us (what we might call ‘no pain, no gain’ theodicies).

In addition, some theists (the so-called sceptical theists) suggest that even if we cannot think of a God-justifying reason for him to allow every last evil we observe in the world, that does not give us good grounds for supposing no such reason exists. They insist there could easily be reasons beyond our ken for God to allow such evils.

So, many conclude, we are not justified in supposing the second premise of the argument – that gratuitous evils exist – is true. But then this argument against the existence of God fails.

Are these responses to the evidential argument from evil adequate? I don't believe so. Compare a different God hypothesis: that there is a single God, but a God that differs from the traditional conception in that this being, while all-powerful and all-knowing, is all-evil. Call this deity Evil God. How reasonable is it to believe in an Evil God?

Notice that, as they stand, many of the most popular arguments for a good God turn out, on closer inspection, to be just as good (or bad) arguments for an Evil God. For they give us no clue as to the moral character of our creator. Teleological or design arguments for the existence of God, for example, typically give us no clue as to whether the cosmic intelligence that is supposed to have created the universe is benign, malign, or morally indifferent, for example. Cosmological arguments for there being some sort of first cause, prime mover or necessary being also typically fail to provide us with any clue as to the moral character, if any, of this being.

And yet almost everyone considers the suggestion that the universe is the creation of an Evil God absurd. Why?

One of the most obvious reasons you might give for rejecting the Evil God hypothesis is that the universe contains far too much good for it to be the creation of such a malevolent deity. Why, for example, would an evil God create love, laughter, ice cream, and rainbows? These things, surely, constitute excellent evidence that there's no Evil God. There's not just good, but at least some gratuitous good, in the universe.

Notice that, in effect, what is being offered here is an argument that mirrors the evidential problem of evil, like so:

A gratuitous good is a good that an Evil God would lack adequate reason to allow. An Evil God might allow some goods if they are the price paid for greater evils. But such a deity won't allow gratuitous goods – goods for which there is no such Evil-God-justifying reason.

But is this a good argument against an Evil God?

Notice that a defender of belief in an Evil God might mirror many of the same moves that we have seen are used against the evidential argument from evil.

For example, a believer in an Evil God may suggest that an Evil God might well have reasons to allow such goods. They may offer mirror theodicies.

For example, they may insist that the many goods that exist are justified from the perspective of an Evil God. Some can be explained as a product of our free will. An Evil God will want moral evil to exist – evil that we freely choose to do. However, by cutting our strings and setting us free, Evil God then allows us to do good – he allows us to work to reduce suffering, for example. This is a good that Evil God may detest, but it's the price he pays to allow the very great evil of moral evil.

Other goods can be explained in terms of (e.g.) not character-building, but character-destroying. For example, an Evil God will create children whom we love so that he can he then kill them on an industrial scale (as he has over the 200,000-year sweep of human history: on average, around a third to a half of each generation of human children have died before reaching the age of five). Ask any parent who has lost a child what is the worst thing they have experienced and they will probably say their own child's death. This deep torment cannot exist unless Evil God creates children, and also love.

Alternatively, instead of explaining away the goods, an Evil God theist might – just like the standard theist – embrace sceptical theism and appeal to mystery. They might argue that even if we cannot think of an Evil-God-justifying reason for him to allow every last good we observe in the world, that does not give us good grounds for supposing no such reason exists. They may insist there could easily be reasons beyond our ken for Evil God to allow such goods.

Still, notwithstanding such ingenious moves to explain away the evidence against an Evil God, can't we reasonably rule out such a deity, and do so on the basis of observation of the world around us?

In effect, I am presenting theists who believe that belief in a good God is by no means unreasonable, while belief in an Evil God is very unreasonable indeed, with a challenge. The challenge – which I have dubbed The Evil God Challenge – is to answer these questions:

Why is belief in good God very significantly more reasonable (i.e. not unreasonable) given that belief in an evil God clearly is very unreasonable indeed?

Why, if we can reasonably rule out an Evil God on the basis of observation of the abundant goods we observe in the universe, can't we similarly rule out a good God on much the same basis – the abundance of evils we observe in the universe?

Surely, some may be tempted to conclude, we can reasonably reject both these two God hypotheses, and on much the same basis: observation of the balance of good and evil in the world – even while admitting that we don't know the answers to such questions as: ‘Why does the universe exist?’ and ‘What accounts for the universe's fine-tuned character?’ Maybe there is some sort of cosmic designing intelligence and/or prime mover behind the universe – perhaps even some sort of god or team of gods – but surely we can be confident that, even if there is some such creator of the universe, it is neither of these two deities.

Two of the articles in this edition of Think engage with the Evil God Challenge.

This issue of Think was edited with help from Molly Selby-Lowndes.