The "Absence of Evidence..." Dodge
In a debate between two people arguing over the merits and proofs of opposing sides, a common rejoinder from an opponent who is trying to make a case for his belief, but has a profound dearth of evidence to support it, would be to say "Absence of evidence is not evidence of absence." I've heard WLC use it when pressed.
One might reply:
No, certainly not, I think we could all agree. But then it is not evidence of presence either. It is not evidence of anything. It makes no assertion about existence, and moves your point no further, either up or down, with regards to being true. It only makes your theory, at most, just as possible as any other theory with no evidence. And if it is uttered in response to another theory supported by evidence, then you have just admitted the shortcomings of your own theory, but waved them away as unimportant because the lack of evidence does not completely disqualify your theory. It seems your standards of proof are extremely low, so low as to already be met. One need only make any claim and the lack of evidence will make it true, or just as valid, in your eyes.
So it seems evidence means very little to you, in principal.
Using "absence of evidence" is especially egregious if it comes on the heels of supposed evidence you have already presented, but, when you find yourself lacking in a particular facet of your argument, you retreat to the "safety in obscurity" of no evidence. You could have saved a lot of time and just said, "There is no evidence, and there doesn't need to be. It's no reason for not taking me seriously." Either you have evidence or you do not. If you do not, you are not allowed to use such a lack as a support for your case.
You change the rules, using evidence when you think it supports your claim, while saying that a lack of evidence also supports your claim, and using gaps in opposing evidence to hide your weaknesses. This smacks of a lack of falsifiability. There is no argument I could make that would prove you wrong, because there is no circumstance under which you will concede that you are wrong.
"Absence of evidence..." can only be used to temporize, to put off judgement until such evidence should be acquired. It loses any relevance when such evidence is, by definition, impossible to collect. To use it as a counterpoint to actual evidence to the contrary makes no sense, and is simply an attempt to dodge the issue of evidence.