Absence of Evidence (The limitations of science)

by John Clinch , London, Thursday, February 28, 2008, 11:40 (6111 days ago) @ George Jelliss

I stand justly criticised. - Re-reading the posting in which I used the rather trite phrase "Absence of evidence is not evidence of absence", I could have expressed myself better. I was making an obvious point badly and I hugely overplayed my hand. I was simply objecting to the dhw's apparent presuppositon that scientists would never uncover evidence about how life could rise from simpler physical forms. His is a hugely strong claim and the irony is that he does not have to make it to justify agnosticism. A classic case of a smart person using a rather silly reason to get to a conclusion that can be propped up in better ways. - But I do need to respond briefly to yours and Mr Whitecraw's epistemological points. The sentence would have made more sense, perhaps, had it read "Absence of evidence is not NECESSARILY evidence of absence". At heart, it's really just Hume's point isn't it? Just because you have experience that something is the case (here, a lack of evidence for abiogenesis) it does not follow as matter of logic or pure reason that you will continue to have that experience. - I disagree with Mr Whitecraw's criticism, though. It is not the argument from ignorance, surely, but its polar opposite. It's an expression of extreme scepticism: it is not saying "You have failed to prove X so Not-X must be true" so much as "You have failed to prove X but X could nonetheless be true". Here, it's saying that, as a matter of logic, we cannot conclude on the basis of our negative experience thus far that abiogenesis is impossible. This is NOT to support any positive point that abiogenesis will happen in the lab, but to criticise dhw for presupposing it to be forever impossible. (Contrary to dhw's posting in this thread, it is a rather important feature of his argument and really goes ot the heart of it). - But I do agree with Mr Jelliss. In the circumstances he outlines, OF COURSE we would be entitled to infer a conclusion about the absense of an elephant in our home. If we didn't use a similar approach to draw conlusions about reality, we could not conduct our lives and science (which is of course based on inductive reasoning) would crumble to nothing. - Incidentally, as to the unaccountable popularity of this expression, I blame the Iraq war when, after the invasion, proponents of the idea that there were WMD were caught saying "Absence of evidence...". The irony is that they later had to face up to the unavoidable conclusions of their own inductive experience: the contiuned absence of evidence BECAME evidence of absence - thus demonstrating the poverty of the phrase and that of purely deductive reasoning generally.