Pattern-chaser wrote: ↑May 11th, 2021, 5:41 amConsul wrote: ↑May 10th, 2021, 11:15 am
As I already pointed out in a previous post, absence of evidence does amount to evidence of absence in case the following condition is met:
1. If p is true, one can reasonably expect to find evidence for p on closer scientific scrutiny.
2. One doesn't find any evidence for p on closer scientific scrutiny.
Weasel words. Yes, there are some very specific and highly constrained examples where absence can be confirmed and verified. This, as we all know, is not the aim or the truth of the statement "absence of evidence is not evidence of absence", which still stands, as it must.
P.S. Reasonable expectation is insufficient; proof is required here. This is rather more formal than a casual chat, which is where "reasonable expectation" belongs.
QUOTE>
"Some slogans regarding evidence are not restricted to particular disciplines but crop up in conversation and sometimes in written discussions on a wide variety of issues. One of these comes in two incompatible forms:
Absence of evidence is not evidence of absence (a statement made popular by Carl Sagan) and
Absence of evidence is evidence of absence.
The first (negative) form is more common, and it is sometimes used in criticism of an argument from ignorance to the effect that one should believe a proposition because its denial has not been proved. It is doubtful whether anyone capable of being swayed by this crude argument could be helped by the slogan. But it is an interesting exercise to determine when the slogan is applicable. The answer appears to be that each version, positive and negative, applies under certain conditions. At a first approximation, we can take the absence of evidence to be evidence of absence—or more broadly and less memorably, we can take the lack of positive evidence for some hypothesis to be evidence against the hypothesis—just in case we have good reason to believe that
if the hypothesis were true, we
would have positive evidence. In one of Sir Arthur Conan Doyle’s stories, Sherlock Holmes finds the key to a mysterious theft in the fact that a dog did nothing in the night, from which he infers that the thief cannot have been a stranger; for if he had been a stranger, the dog would have been expected to bark during the intrusion. On the other hand, in some cases we would not expect to have positive evidence regardless of whether the hypothesis is true or false. Spontaneous proton decay, if it takes place at all, is an event so rare that our expectation of catching it happening is nearly zero. Consequently, our failure thus far to detect it does not give us much in the way of a reason to reject the theoretical possibility. One advantage of looking at the slogan in probabilistic terms is that the first approximation can be sharpened: ~E is evidence for ~H just in case P(E|H)/P(E|~H) > 1; and the stronger the inequality, the better the evidence. This formulation has the merit of drawing attention to the fact that E may be strong evidence for H, even when both P(E|H) and P(E|~H) are quite small in absolute terms, provided that their ratio is very large."
(McGrew, Timothy. "Evidence." In
The Routledge Companion to Epistemology, edited by Sven Bernecker and Duncan Pritchard, 58-67. New York: Routledge, 2011. pp. 64-5)
"Genuine Evidence: Pr(E|H) > Pr(E|¬H), so that the evidence we’re looking for is evidence for H. It follows that Pr(¬E|¬H) > Pr(¬E|H).
...
It is a well known consequence of Bayesian confirmation theory that if Pr(E|H) > Pr(E|¬H), then E confirms H. It similarly follows that if Pr(¬E|¬H) > Pr(¬E|H), then ¬E confirms ¬H. The Genuine Evidence condition states that the antecedent of this latter conditional is true, and so in such cases we should expect that ¬E confirms ¬H. But this is just to say that the absence of evidence (¬E) is evidence of absence (¬H)."
(Stephens, Christopher. "A Bayesian Approach to Absent Evidence Reasoning."
Informal Logic 31/1 (2011): 56-65. pp. 61-2)
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