I keep hearing this koan-like statement. It's not true. Consider this counter-example:
- I suspect that my kid is smoking dope (because of that damn rap music he listens to). To prove my hunch, I search the house from top to bottom. I find no stash. While he's asleep, I take a hair sample and send it to a lab. The test comes back negative. I hire a team of private eyes to follow him 24/7. They find nothing.
There is an absence of evidence here. If this does not, in addition, constitute "evidence of absence", what would? What further evidence would be required to demonstrate that my son is not smoking dope, the testimony of an omniscient being?
I am _not_ suggesting that the above scenario is in any way analagous to the hunt for WMD. My point is that the absence-of-evidence talisman is bunk. I suspect that this silly tongue-twister was initially coined with the intention of inducing cerebral paralysis, thereby nipping discourse in the bud. To that sordid end it has worked wonders.
Part of the problem is that this reasoning could be used in defense of utterly absurd positions:
- I contend that purple crows exist. Since no one has ever seen such crows and ornithologists swear they do not exist, I will reluctantly grant that there is an absence of evidence for my contention. But as Rumsfeld and everybody else keeps telling us "absence of evidence is not evidence of absence."
This expression is not one of logic's Ten Commandments and has no place in geopolitical discourse. We could perhaps ask "At what point does an absence of evidence become evidence of absence?" but then we're doing conceptual analysis and might as well tackle the all-time gem "Is the difference between a difference of degree and a difference of kind a difference of degree or a difference of kind?" I think both questions are in the same ballpark regarding their practical application.
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?