Problem of Evil

Leibniz's solution to the problem of evil

James Franklin

Think 5 (Autumn 2003), 97-101

Mark Piper's article 'The perennial problem of evil' (Think 4) summarises received ideas on the question. They are:

• It would be a moral disgrace for God (if he existed) to allow the many evils in the world, in the same way it would be for a parent to allow a nursery to be infested with criminals who abused the children.

• There is a contradiction in asserting all three of the propositions: God is perfectly good; God is perfectly powerful; evil exists (since if God wanted to remove the evils and could, he would).

• The religious believer has no hope of getting away with excuses that evil is not as bad as it seems, or that it is all a result of free will, and so on.

Piper avoids mentioning the best solution so far put forward to the problem of evil. It is Leibniz's theory that God does not create a better world because there isn't one — that is, that (contrary to appearances) if one part of the world were improved, the ramifications would result in it being worse elsewhere, and worse overall. It is a "bump in the carpet" theory: push evil down here, and it pops up over there. Leibniz put it by saying this is the "Best of All Possible Worlds". That phrase was a public relations disaster for his theory, suggesting as it does that everything is perfectly fine as it is. He does not mean that, but only that designing worlds is a lot harder than it looks, and determining the amount of evil in the best one is no easy matter. Though humour is hardly appropriate to the subject matter, the point of Leibniz's idea is contained in the old joke, "An optimist is someone who thinks this is the best of all possible worlds, and a pessimist thinks

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the same." And it is in tune with the obvious thought: "If God is doing his best, then this must be the best he can do."

No-one would maintain that this is a plausible theory, at first glance. Everyone thinks they could do a much better job than the present shambles, given enough power. Let us first note, though, that the barest possibility that Leibniz is right is enough to dispose of the second of the received ideas above, the alleged logical incompatibility of God's goodness, God's perfect power, and the existence of evil. To show propositions are logically compatible, all that is needed is to exhibit a merely possible scenario in which they are all true. In Leibniz's Best of All Possible Worlds scenario, they are all true. Therefore, the three propositions are compatible.

To see why we should doubt our initial feeling that it is easy to imagine a better world, we need to remember that perfect power comes with perfect knowledge, in particular, perfect knowledge of how things constrain one another, of how doing this here makes doing that there impossible. There are many examples in the "formal sciences", the disciplines like operations research, control theory, statistics and theoretical computer science that have emerged in the last sixty years at the interface between mathematics and engineering. The flavour of these results is easily seen in the first investigation of this kind, Euler's eighteenth-century paper on the bridges of Königsberg. The citizens of Königsberg noticed that it seemed to be impossible to walk across all seven bridges over the River Pregel, without walking across at least one of them twice:

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Figure 1: The Königsberg bridges

Euler proved mathematically that they were right: though it is easy at any point to choose a bridge to walk over, it is absolutely impossible to perform the whole task as a whole. Although God could make bridges, islands or citizens differently, he could not make them the same while at the same time making it possible for the citizens to walk over all the bridges once and once only.

That is only one example, of course. There are many such, well appreciated by mathematicians, engineers, planners and architects. Philosophers are possibly the worst people to appreciate them, as most philosophers have never built, let alone designed, so much as a model aeroplane. They therefore find it easy to write, as Piper does, "an all-powerful God, by definition, would be able to achieve the end (the greater good) without using the means (the evil)." Not so fast. Good and evils can be more intimately and necessarily connected than that. That, indeed, is the real point of the "free will defence". It is not remotely plausible that all instances of evil can be explained away as effects