The mystical security guard
February 17, 2015 — 10:58

Author: Alexander Pruss  Category: Problem of Evil  Tags: , , ,   Comments: 8

One objection to some solutions to the problem of evil, particularly to sceptical theism, is that if there are such great goods that flow from evils, then we shouldn’t prevent evils. But consider the following parable.

I am an air traffic controller and I see two airplanes that will collide unless they are warned. I also see our odd security guard, Jane, standing around and looking at my instruments. Jane is super-smart and very knowledgeable, to the point that I’ve concluded long ago that she is in fact all-knowing. A number of interactions have driven me to concede that she is morally perfect. Finally, she is armed and muscular so she can take over the air traffic control station on a moment’s notice.

Now suppose that I reason as follows:

  • If I don’t do anything, then either Jane will step in, take over the controls and prevent the crash, or she won’t. If she does, all is well. If she doesn’t, that’ll be because in her wisdom she sees that the crash works out for the better in the long run. So, either way, I don’t have good reason to prevent the crash.

This is fallacious as it assumes that Jane is thinking of only one factor, the crash and its consequences. But the mystical security guard, being morally perfect, is also thinking of me. Here are three relevant factors:

  • C: the value of the crash
  • J: the value of my doing my job
  • p: the probability that I will warn the pilots if Jane doesn’t step in.

Here, J>0. If Jane foresees that the crash will lead to on balance goods in the long run, then C>0; if common sense is right, then C<0. Based on these three factors, Jane may be calculating as follows:

  • Expected value of non-intervention: pJ+(1−p)C
  • Expected value of intervention: 0 (no crash and I don’t do my job).

Let’s suppose that common sense is right and C<0. Will Jane intervene? Not necessarily. If p is sufficiently close to 1, then pJ+(1−p)C>0 even if C is a very large negative number. So I cannot infer that if C<0, or even if C<<0, then Jane will intervene. She might just have a lot of confidence in me.

Suppose now that I don’t warn the pilots, and Jane doesn’t either, and so there is a crash. Can I conclude that I did the right thing? After all, Jane did the right thing—she is morally perfect—and I did the same thing as Jane, so surely I did the right thing. Not so. For Jane’s decision not to intervene may be based on the fact that her intervention would prevent me from doing my job, while my own intervention would do no such thing.

Can I conclude that I was mistaken in thinking Jane to be as smart, as powerful or as good as I thought she was? Not necessarily. We live in a chaotic world. If a butterfly’s wings can lead to an earthquake a thousand years down the road, think what an airplane crash could do! And Jane would take that sort of thing into account. One possibility was that Jane saw that it was on balance better for the crash to happen, i.e., C>0. But another possibility is that she saw that C<0, but that it wasn’t so negative as to make pJ+(1−p)C come out negative.

Objection: If Jane really is all-knowing, her decision whether to intervene will be based not on probabilities but on certainties. She will know for sure whether I will warn the pilots or not.

Response: This is complicated, but what would be required to circumvent the need for probabilistic reasoning would be not mere knowledge of the future, but knowledge of conditionals of free will that say what I would freely do if she did not intervene. And even an all-knowing being wouldn’t know those, because there aren’t any true non-trivial such conditionals.

  • Michael Almeida


    In the case of evils that God allows, they are typically understood as necessary to some greater good. So, we’ll need to assume that the crash is necessary to some greater good. You might reason this way: there is simply no other way to achieve that greater good than to allow the crash, and so I am permitted to allow it. Otherwise I will preclude the possibility of that good, which surely I’m permitted to allow. On the other hand, if the crash is not necessary to a greater good, then God could not allow it.He could actualize that greater good without the crash. On a still third possibility, the crash is necessary to a greater good, but God does not want that greater good. In that case again, He cannot allow it. As you describe the case, it is ambiguous between these cases. But, however it works out, you are permitted to allow the crash.

    February 17, 2015 — 13:12
    • It need not be the *crash* that is necessary to a greater good. What may be necessary to the greater good is *allowing the possibility of the crash*.

      February 17, 2015 — 14:21
      • Michael Almeida

        I don’t think that can be right. Possibilities are not the sort of things that are allowed or not, except trivially. What’s possible is necessarily so.

        February 17, 2015 — 15:07
  • Alexander Pruss

    Metaphysical possibilities are necessarily possible. But this is not true for other kinds of possibility.

    February 17, 2015 — 16:12
  • Michael Almeida

    I can’t follow that. Is the claim that the causal possibility of the plane crashing is metaphysically necessary to a greater good and the causal possibility of the plane crashing is up to God? But God does not determine what’s causally possible either. If it is causally possible that the plane crash, then there is some world consistent with our laws in which the plane crashes. Nothing God can do about that. He can’t make it the case that there are no such worlds. Or maybe it’s my ability to crash the plane that is necessary to a greater good. But there is nothing God can do about that either. If I’m able to crash the plane, then there is nothing God can do to make it the case that I am unable to do so.

    February 17, 2015 — 16:39
  • Michael Almeida

    For what it’s worth, it’s probably true that the proposition expressed by ‘it is causally possible that the plane crashes’ is also necessarily true, if true at all. It just expresses the proposition that it is consistent with the laws L that the plane crashes, and that is true in every world.

    February 17, 2015 — 16:46
  • Mike:

    I was just giving a loose way of putting the expected utility argument in the post. The point there is that pJ+(1-p)C can be positive even if C is negative.

    February 18, 2015 — 9:03
  • Michael Almeida

    I was definitely reading it too closely. That conclusion is probably right.

    February 18, 2015 — 10:39
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