Absence of evidence IS evidence of absence

I think that, within clearly defined constraints, absence of evidence can be evidence of absence. It man be weak evidence, or it may be strong evidence.If you define a search target, and define a search area - Doing a rigorous search of that area, and not finding that target in that area, would surely be evidence that the target does not exist in that area. This is not to say that a differently defined target does not exist in that area, or that a same defined target does not exist in a different area.As I have followed this topics discussion, that seems to be (at least generally) DNA's line of reasoning.Moose

I agree that that's a valid and reasonable method, but you'll have to show me where DNA said that. Especially the part about defined search areas.

I think we never got to that much detail. Everyone just kept arguing about if AoE could be EofA without getting clear what criteria there might be for AoE being good, bad or so-so evidence. If you want to firm that up a bit now it might be a good idea.

Well then I propose that if you don't know where something would be if it existed - if you don't know where to look - then absence of evidence in the places you've looked is not evidence of absence - it's evidence that you haven't looked in enough places.

Hey Crash,I've been following the discussion pretty closely. DNAunion has a point (never thought I'd agree with anything he writes - we have a long history from IIDB). Absence of evidence CAN be taken as evidence of absence. At some point in the search for evidence, after repeated failures, it becomes problematic that any further search will be fruitful. Although the point is arbitrary, at that moment we can tentatively state that the lack of supporting data or observation indicates that the phenomenon or whatever probably doesn't exist - which is the basis for my opinion that supernatural deities don't exist. OTOH, absence of evidence CAN NEVER be taken authoritatively as evidence for absence. That might seem like a semantic difference, but it is a crucial one. Interestingly, it appears from the OP and from other threads that DNAunion IS assuming the "for" conjunction, although never explicitly stating this. He is very careful to verbalize the difference, but in practice seems to ignore it. Which is historically very typical of his debate style.

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I agree that that's a valid and reasonable method, but you'll have to show me where DNA said that. Especially the part about defined search areas.

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I reviewed through parts of the topic, and I think there are at least hints of DNA's touching on it. His rather muddled writting style certainly doesn't help things. I think part of the situation was, that you were reading his posts with the "find him wrong" filter engaged, while I was reading them with the "find him right" filter engaged.Anyhow, I find that the "car keys in the kitchen" discussion may illustrate the situation. I believe it started at Marks message 36.I must find some irony in that it seems that it took until my message 76, to come to a clear, concise statement on it all. And I didn't even get a "Post of the Month" out of it. Moose

I agree completely, minnemooseus. It depends on the sample size; the basic logical fallacy exists when someone attempts to apply it to a situation in which only a miniscule percent of the total set has been examined.BTW, I like your avatar. ------------------
"Illuminant light,
illuminate me."

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You can use an absence of evidence as evidence of absence when you're pretty damn sure you'd know where the evidence would be, if it existed at all

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That's not absence of evidence, it IS evidence.If you KNOW that for A to be true you MUST find B under
condition X, and you don't that is evidence against A.That's not the same thing at all.If for A to be true B must exist somewhere, under some
unspecified condition, and you do not find B, it tells
you NOTHING (except to look elsewhere).

If I search a house and don't find anyone inside,
can I conclude that the house is empty?

That does seem to be the line of reasoning ... but
it doesn't make absence of evidence evidence of absent,
it just changes the rules.If you are looking for something (A) in a well-defined search space
and you know that you have covered 100% of that space without
finding (A) then the absence of (A) has been shown.If you have not covered 100% of the search space, you have not
shown the absence of (A).You may, as your coverage increases, become convinced that you
will never find (A) ... but the accumulation of failed searches
does not amount to evidence that (A) is not present (nor that
it IS present).I think what is beign suggested is that the longer something
remains absent of evidence, then that builds a case for
the absence.This is not true. One can never rule out that one is
looking in the wrong place or for the wrong thing except in the
extreme case where the issue is so well defined that the
entire search space can be investigated with 100% coverage and
100% certainty of success were IT there.E.g. the football field -- we cannot say the field is absent of
a football until we have searched every football sized space
on the field.Things are always in the last plave you look for them

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If you are looking for something (A) in a well-defined search space and you know that you have covered 100% of that space without
finding (A) then the absence of (A) has been shown.

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You don't say such, but the above assumes that the nature of (A) is also well defined.Regardless, is not the absence of any evidence of (A) being in the well defined search area, indeed the evidence of (A)'s absence in that area?Moose

You are quite right that (A) has to be well defined too.And yes, the absence of evidence is, in that extreme case,
evidence of absence ... but only because the nature of the
search is so well defined and bounded.Until you reach 100% coverage of the search space you have
no evidence at all.You could say that (A) is becoming unlikely (that probably equates
to Absence of evidence not being proof of absence), but as soon
as you relax the definition of (A) and/or the search space
all bets are off.If you don't know how much of the search space you have covered,
or you don't sufficiently understand the nature of (A) then no
amount of absence of evidence is indicative of actual absence.

In the context of this forum, the "absence of evidence..." theme comes up (mostly, as I see it) in two areas:1) The existence of God.Here we suffer from trouble defining the nature of the search object. The search area has a simular problem. You could define it as some finite area, but the true area needing to be searched seems to be the entire universe (and beyond?). Conclusion: Absence of evidence is not evidence of absence.2) The existence of transitional fossils.I think we can pretty well define the nature of the search object (although the creationist side might disagree). We can also pretty well define the search area, although it would be pretty vast, with most of it buried in the earth.The catch for fossils, is that many critical juncture transitional fossils may never have been preserved in the first place, or may have been destroyed though the recycling processes of geological activity.Of course we can never know for sure, but a given transitional fossil may truly not exist, despite the fact that the life form did exist. Thus we may indeed have an absolute absence of evidence - but while this might be an evidence for the absence of the fossil, it isn't an evidence for the absence of the life form having existed.Boy, my best babble in a long time,Moose

Yes.It's about the relationship of the evidence to the object being
sought.