Saturday, December 04, 2010

Absence of Evidence

In the comments thread to a post on another blog, a commenter gave the following quotation:

'The simplest explanation for the total absence of evidence for gods is a total absence of gods'.

I've increasingly over the past couple of years come across claims of this sort (the commenter seems to be quoting someone, but I don't know who), and I find it interesting because the underlying idea seems to be pretty clearly wrong, for all its superficial plausibility, even when we ignore the obvious hyperbole of 'total absence of evidence'. (Obviously there's evidence -- religious experiences, etc.; the question is just whether it's adequate to establish the conclusion. It is very rare to find cases of actual disputes where one side literally has no evidence at all, inconvenient as that fact may be. Even believers in house elves have strange occurrences to call to witness. What we usually mean is that the evidence is weak, which is very different from being nonexistent. The rhetorical advantages of conflating weak evidence with no evidence are, of course, obvious; but we should not treat a rhetorical figure as literal speech.) What we mean by "total absence of evidence" is at most a total absence of evidence available to be used in reasoning (otherwise the only way to establish total absence of evidence for X is to prove that X can't possibly exist -- if we aren't talking about evidence available to us, we'd have to take into consideration all evidence available to everyone at every time, including the future, and therefore we would need to establish a guarantee that no real evidence could possibly turn up in the future). And because of this, if all other things are equal, the simplest explanation for absence of evidence is that you've probably just overlooked it or not come across it. It is simplest in at least three different ways:

(1) It involves the weakest supposition about the world. If I commit to the claim that some evidence of X probably exists, I'm not by that committed to any claim for or against the existence of X, just to the existence of something that someone could reasonably classify as evidence for the existence of X, whatever that evidence might be. This is clearly a weaker supposition, with fewer commitments, than the supposition that there is no X.

(2) It is the simplest in that, unlike a categorical rejection or affirmation of something's existence, it allows for the subsumption of the case under an already well-established generalization, that is, the straight psychological fact that people often overlook or fail to come across evidence for things.

(3) It is the simplest in that it provides the least impediment to future inquiry: it closes down the fewest options for further research.

Part of the problem, I think, is that phrases like 'total absence of evidence for the existence of X', despite the literal meaning, actually convey in practical, colloquial speech the idea that there is, overwhelmingly, evidence against the existence of X, and it is indeed true that the simplest explanation for overwhelming evidence against the existence of X is X's nonexistence. And perhaps a failure to recognize that we do not, in actual practice usually judge absence of evidence absolutely but relative to what is accessible to us (the distinction I mentioned above) contributes to this confusion. But what is actually happening is that an entire range of suppositions is being elided. And there's a reason why people often say that absence of evidence is not evidence of absence: it's precisely that actual absence of the thing/event/whatever is not the simplest explanation for absence of evidence, considered on its own.

There are actual cases where an absence of evidence would be evidence of absence, of course; the cases, that is, where all other things are not equal. In practice, all of these are cases where we actually have pre-existing preponderant reason (either through preponderance of evidence or through actual proof) that X's existence is inconsistent with the lack of evidence in question, or else made definitely unlikely by it, and that it is either impossible or unlikely that the reason the evidence is lacking is your fault. But these cases, of course, don't salvage the general principle.


  1. Jarrett Cooper9:36 PM

    I too read that same comment earlier today.

    I'm curious to know how Pruss will respond. Either kindly show the poster that there are reasons or 'evidences' to believe in God, or he'll simply not respond to the post. It's kinda' hard to know where to begin with a comment like that. 

  2. Isn't another, possibly larger problem in that discussion the claim how "we see the universe naturalism predicts"? What universe does naturalism predict? One of this size? Is life supposed to be easy and common under naturalism, or difficult and extremely rare? (Should we expect it to exist at all?) Should universes be large or small? What fundamental forces should be at work? What special sciences? (Should there be any of these at all?)

    In fact, I'd say this is related to the "total absence of evidence for gods" line. I often get the impression that the "total lack of evidence" is in part claimed because the (unspoken) evidence being looked for is "something I can't give at least some kind of naturalistic explanation for, no matter how unlikely or brute". Forgetting for a moment that "naturalism" seems to have very little content to it other than denying God's existence (and then, mostly the God of the Abrahamic faiths particularly), that seems like a ridiculously low hurdle to jump. Along the lines of saying there's a total lack of evidence for psychology, on the grounds that scientologists can offer up alternate explanations for every detail a psychologist would explain.

  3. branemrys1:38 PM

    Perhaps, but this seems to be something that arises more from the faulty terms of the dispute than from anything to do with naturalism itself; one could run parallel arguments with regard to the theistic side.

  4. Maybe it could be run against theism, but I think that would just highlight the problem further. Do you yourself think there is a "way the universe should look given naturalism", I wonder? As opposed to "an explanation for the universe that could be thought up that makes no reference to God".

  5. branemrys5:45 PM

    No, but there's no "way the universe should look given theism," either; since both actually start from the universe as it appears to be and aren't pulled at random out of a heaven of disembodied hypotheses, the only sense that can be given to either is, "the way the universe does in fact look." It's thinking in terms of probabilities of events given hypotheses, and of hypotheses given events, that is at the root of the problem. Further, even if this were set aside, both theism and naturalism are categories too diffuse and diverse to make it reasonable to say much about what would be the case if one or the other were true: fully developed positions, with all their details, are what actually explain and anticipate, and every theist's theism and every naturalist's naturalism will have scores of auxiliary claims that would really be doing the lion's share of the work. The problem here really seems to me to lie with the dialectical conventions of contemporary philosophy rather than with any particular position.

  6. Well, I'm not arguing that theism somehow performs better in the "way the universe should look" claim. (I'm not conceding the point either, it's just not my point here. Though if there's no "way the universe should look given atheism" or "...given naturalism", then it becomes hard to tell how it should look given theism, at least in some ways.)

    I appreciate your point when you note that "both actually start from the universe as it appears to be". I just think that, like the line you quoted at the start, the "universe looks the way it was if atheism/naturalism were true" is oft-repeated but has little substance.

    Just a comment in passing, and I enjoyed the post otherwise, so pardon my distraction.

  7. branemrys8:48 PM

    Oh, no, I think you're quite right about its being uncritically reiterated; it's just that the point the post is about seems to be more self-standing, while the one you're noting seems to have roots that run much deeper and are therefore both hard to trace and entangled in a wider variety of perspectives.


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