Absence of Evidence is Evidence of Absence

[MorpheusSandman]

The only case Rummy missed was the one about those unknowns that we know.

He actually mentioned that (as Emil said). Zizek suggested one Rummy missed though, the unknown known: "If Rumsfeld thinks that the main dangers in the confrontation with Iraq were the "unknown unknowns", that is, the threats from Saddam whose nature we cannot even suspect, then the Abu Ghraib scandal shows that the main dangers lie in the "unknown knowns" – the disavowed beliefs, suppositions and obscene practices we pretend not to know about, even though they form the background of our public values."

[MorpheusSandman]

Sorry, double post (moderator can delete).

[YesNo]

You haven't been paying attention to what Rummy was saying. He distinctly mentions known unknowns just before he refers to unknown unknowns. Now if he had said there are known unknowns that we know are known or unknown knowns that we don't know are unknown that would have answered all queries relating to the problem; except for those unknown unknowns that we don't know are known.

Thanks for setting me straight, Emil Miller and MorpheusSandman.

Actually, Rummy doesn't make any more sense to me today than he did a decade ago, but that could be related to my pigheaded inability to see WMDs where there weren't any.

[Emil Miller]

Thanks for setting me straight, Emil Miller and MorpheusSandman.

Actually, Rummy doesn't make any more sense to me today than he did a decade ago, but that could be related to my pigheaded inability to see WMDs where there weren't any.

Well, you know what they say: Absence of evidence isn't evidence of absence. Or in the case of WMDs, really was evidence of absence.

[Delta40]

So Morph is this a valid argument for the existence of god?

[MorpheusSandman]

So Morph is this a valid argument for the existence of god?

If absence of evidence is evidence of absence then it's a valid argument AGAINST the existence of God, since there's no (valid) evidence for his/its existence. The opposite phrase, EOA IS NOT AOE is usually used by believers to argue that the AOE for their God isn't evidence of his/its absence.

[Delta40]

Thank god for that!

[MorpheusSandman]

Thank God I'm an atheist. -- Luis Bunuel

[YesNo]

1. If the thing doesn't exist the probability of there being a continuing absence of evidence is 100%
2. If the thing exists the probability of there being a continuing absence of evidence is less than 100%

(1) is incorrect. That is what I thought the WMDs in Iraq illustrated (or the existence of nonexistent clothes on the Emperor). We have a history of finding evidence for the existence of stuff that doesn't exist if we want to bad enough. So (1) should be less than 100% for some nonexistence stuff.

(2) is even incorrect. The existence of specific creatures in other universes (coming from other big bangs which I assume happened since our big bang happened) is something we will never know at least by currently acceptable means. So there exist things for which we will never have evidence of their existence and (2) will stay at 100% for them.

[Ecurb]

Good points, YesNo. In my previous Sasquatch example there is an absence of certain kinds of evidence (which is sufficient to persuade me that there are no Sasquatches), but there is plenty of evidence supporting the notion that Sasquatches exist. If we think of facts about the past (to return to the Julius Caesar example) there are a great many things that happened in the past for which no evidence exists, or ever will exist. What did Joe Blow have for dinner on May 19, 1211? In this case, the absence of evidence does not persuade me that Joe went hungry, because we would not expect to have any evidence about such a trivial fact.

So although absence of evidence CAN BE evidence of absence, it is not NECESSARILY evidence of absence. I suppose morpheus could argue that there is a infinitesimal possiblity that we might some day discover what Joe Blow (or some individual T-rex 100 million years ago) had for dinner in the distant past, if he ate dinner, so the absence of evidence constitutes infinitely weak evidence for fasting. But this seems like a distinction without a difference.

[Paulclem]

I reckon this thread should be called "The Emperor's New Absence".

[YesNo]

Taking the example of what Joe Blow had for dinner in 1211 is better than my other universe example, Ecurb. Unless we invent a time machine (which I highly doubt), we shouldn't be able to find this out.

I was thinking about Sasquatch when you mentioned him or her earlier in this thread. It all depends on how one defines "Sasquatch" as to whether examples exist or not. For example, Wikipedia says (http://en.wikipedia.org/wiki/Sasquatch) Bigfoot is "large, hairy, bipedal humanoid". Well, a human is a humanoid by default and most of us are bipedal. Some of us are hairier than others and some of us can get quite large. So maybe Sasquatch is a subset of the human species who likes to walk through the woods and is larger than most of us get.

[Nick Capozzoli]

Well it's quite true, they did have wireless communications. Communication was by runner with a piece of knotted string or a cleft stick

And that was part of the point I was trying to make with the joke... "Wireless" communication is a broad term, but we take it to mean "radio" communication, though of course that would include every other form of communication that doesn't involve sending and receiving electrical signals over conductive wires.... The joke was a bit off topic, but not entirely... To be on-topic, the archeologist should not conclude that the absence of found wires indicates anything more than that the ancient Peruvians (probably) did not use electrical wires. It was just a joke meant to illustrate sloppy reasoning. In fact, the archeologist would have more logically concluded that the lack of evidence for wires indicated that the ancient Peruvians had no electrical technology whatsoever, let alone radio technology. Would it still be possible that they did have some electrical technology? Perhaps, though the burden of proof would be on the one making that assertion.

[MorpheusSandman]

(1) is incorrect. That is what I thought the WMDs in Iraq illustrated (or the existence of nonexistent clothes on the Emperor). We have a history of finding evidence for the existence of stuff that doesn't exist if we want to bad enough. So (1) should be less than 100% for some nonexistence stuff.

(2) is even incorrect. The existence of specific creatures in other universes (coming from other big bangs which I assume happened since our big bang happened) is something we will never know at least by currently acceptable means. So there exist things for which we will never have evidence of their existence and (2) will stay at 100% for them.

(1) Incorrect. What you're talking about gets into the nature of "what is evidence?" rather than if evidence exists for non-existing things. It's true that certain information can LOOK like evidence for non-existing things, but because these things are non-existent, it's our interpretation of the information that's at fault, because it's not really evidence for the thing we think it is. That's why it's important to have a good grasp/understanding of what evidence is before one starts talking about whether such-and-such piece of evidence is evidence at all. To go back to Ecurb's Sasquatch example, one hidden assumption behind the "absence of evidence" phrase is that people aren't faking evidence to begin with, and when it comes to things like Sasquatch, that's not necessarily true. This relates to one Yudkowsky article that nicely summarizes this by saying "we'd expect UFO cults whether UFOs existed or not, so the existence of UFO cults are not evidence UFOs exist." Same with Sasquatch footprints; we expect them because we know certain people believe they exist and want to convince others.

(2) Incorrect again, because you're making multiple assumptions that you can not be 100% sure of:

a) other universes exist
b) other creatures exist in these universes
c) we will never have any evidence about the nature of these other universes

So even when you consider the probabilities of these three things you can't set 2. at 100%, because then you'd just be assuming things you have no reason to assume. But, even if I was to grant your assumption, I think it's safe to say that we're most always only concerned about things that exist within our universe OR things that may exist outside our universe but affect our universe in some way or another. In both cases there would be evidence of their existence.

[MorpheusSandman]

So although absence of evidence CAN BE evidence of absence, it is not NECESSARILY evidence of absence. I suppose morpheus could argue that there is a infinitesimal possiblity that we might some day discover what Joe Blow had for dinner in the distant past...

Taking the example of what Joe Blow had for dinner in 1211 is better than my other universe example, Ecurb. Unless we invent a time machine (which I highly doubt), we shouldn't be able to find this out.

Now you guys are having the same difficulty Hawkman had in coming up with examples that aren't even relevant to the phrase itself. "Evidence of absence" means "evidence that something exists/existed," not "evidence that someone once ate something" or "evidence that someone will eat something" or (to use Hawkman's example) "evidence that something can be invented that doesn't currently exist." You guys need to think about examples of things that exist NOW or DID for which there COULD be evidence for. Obviously people eat and the "evidence" of what they eat gets digested and disappears; obviously we can't have evidence NOW for what someone will eat; obviously there would be no evidence now for what someone might invent in the future; all of these things have nothing to do with the phrase itself or what it pertains to. My dice example, or coin example, or book example, et al. pertains to things that potentially exist now and would potentially leave evidence for itself existing.

Just as I said in my last post that one hidden assumption in the phrase is that people aren't faking the evidence, another assumption is that there would/could be some kind of evidence for the thing that exists/existed. Instead of what someone ate 30 years ago, consider, instead something like a global flood, a myth present in many cultures in texts; if such a thing happened, we'd expect certain Geological evidence for it; yet, not only is there no evidence for such a flood, there is evidence of erosion at varying rates in different parts of the world, which is what you WOULDN'T expect if such a catastrophic event happened on a global scale. That's a legitimate example from something in the past because it's something that we would expect to leave evidence were it true. Things people ate or might eat or things we can invent don't leave evidence for itself now, so the phrase is rather irrelevant.

I guess it's my fault for not clarifying this in the OP, but I thought these assumptions were rather implicit. So, for full disclosure, here are the relevant details:

1. Something potentially exists now, or existed/happened in the past.
2. Something that would/could leave evidence for itself

Any talk of "future" events/things is not relevant, nor are things that we know leave no evidence for their existence, like what Joe Blow ate 30 years ago.