Yes it is. For example, right now I have no tangible evidence whatsoever that the moon exists (it being daytime where I live, I don't live near the sea to be able to observe tides, I don't have photos of the moon as my PC background or on my wall somewhere, etc.) Shall I start to doubt the moon's existence, then?
That is sophistry.
I will grant, I suppose, that it's conceivable one can construct detailed, complicated examples where Absence Of Evidence seems to legitimately throw more weight behind the "It's Absent" theory. Presumably, that is what you are about to do in your post. Sigh.
P.S. What is "koan-like"?
While he's asleep, I take a hair sample and send it to a lab. The test comes back negative.
Sorry, you screwed up, and so early on too. This isn't an "absence of evidence"; an "absence of evidence" would exist if you had never been able to get your hands on a hair sample in the first place. What you've got here is positive evidence that his system has been clean from dope for the past X days... (that's what such hair tests tell you, as I understand them).
I hire a team of private eyes to follow him 24/7. They find nothing.
Also not an "absence of evidence". An "absence of evidence" would exist if you had no idea what he was doing during certain parts of the day. Here, you've got PIs observing his behavior "24/7". If that's really true you can actually have positive eyewitness testimony to statements like "he definitely did not light up in the past X days".
I am _not_ suggesting that the above scenario is in any way analagous to the hunt for WMD.
Good.
My point is that the absence-of-evidence talisman is bunk.
First it was "koan-like", now it's a "talisman"?? Couldn't you just use "cliche" like a normal person? ;-)
Anyway, it's not "bunk". Your examples are.
Part of the problem is that this reasoning could be used in defense of utterly absurd positions:
That's true and no one, least of all me, would deny that.
This expression is not one of logic's Ten Commandments and has no place in geopolitical discourse.
I don't know whether we're participating in "geopolitical discourse" here, whatever that is, but it does have a place in a discussion where one side is acting like a proposition (Iraq had no WMD) has been proven.
I think both questions are in the same ballpark regarding their practical application.
Very well. I'll make a note of that in my records. (rolls eyes)
So, you think Iraq had no WMD, or not?
Specious. To doubt that the moon exists you would need to question either the veracity of your memory or whether nature will continue to work the way it has in the past. Theoretically you can doubt both, but I don't think you can really doubt them. In place of "the moon" substitute "Bigfoot", "Zeus", "ghosts", "extraterrestrial visitors" and you not only can doubt their existence, you should - given the dubious evidence. Should we remain agnostic about Zeus & Bigfoot because new evidence could come in? It's a fundamental mindset: no evidence for X = don't believe X. Some of us go through life like this (or at least aspire to - it depends a great deal on how one defines "evidence" and there are some beliefs we're hard-wired to have).
A koan is a puzzling, paradoxical statement used in Zen Buddhism to snap the student out of his rational ways of thought (What is the sound of one hand clapping?) The Absence of Evidence line struck me as being designed to obfuscate, not clarify. It isn't some Universal Logical Truth, though that's the implication. And it isn't a cliche - yet.
...it does have a place in a discussion where one side is acting like a proposition (Iraq had no WMD) has been proven.
This proposition can never be proven, only disproven - very easily. But the more we try to disprove it and fail the more reasonable it becomes to abandon agnosticism and add WMD to the Bigfoot/Zeus category.
So, you think Iraq had no WMD, or not?
They certainly did at one time. Did they recently have massive stockpiles? My fingers are crossed. For one simple reason I hope not: If they did, and we can't find them now, one very likely explanation is that someone else has them.