Ignorance Of Evidence Is Not Absence Of Evidence

Several folks over on the AbsenceOfEvidenceIsNotEvidenceOfAbsence page have noted that the corresponding saying, originally attributed to Carl Sagan, is actually false according to the rules of empirical science and evidence. Absence of evidence is in fact evidence of absence. It's just not the same thing as proof, and neither is lack of personal knowledge of something the same as evidence of it's absence.

Absence of evidence is only "evidence" of absence if one has gone about making a reasonable attempt to gather such evidence (most likely beyond simply their own immediately recollectible experience). In that case, one has actually made the effort to look and found no evidence -- they have found evidence of the absence of evidence. Otherwise, there is no known absence of evidence, only ignorance of evidence or ignorance of the absence of evidence.

The statement "AbsenceOfEvidenceIsNotEvidenceOfAbsence" is talking about the cases where someone simply "off the cuff" says something like "well, Ive never seen it" or "I havent seen it in my experience." That's a far cry different from making a concerted effort across numerous sources too look for it and then coming up empty handed. It's little more than an illegitimate excuse to keep a closed-mind closed.

The real problem being addressed by the (perhaps oxymoronic, or just plain moronic :-) phrase is that IgnoranceOfEvidenceIsNotAbsenceOfEvidence. The phrase "AbsenceOfEvidenceIsNotEvidenceOfAbsence" may in fact be logically incorrect according to the rules of empirical science. However, it's intended meaning (from both the original source and others on this Wiki that use it) is indeed what the top of that page says: Lack of knowledge/experience/awareness of something (which is a polite way of saying "ignorance") does not imply lack of existness/correctness. Ignorance of evidence is not the same as the "absence" of evidence, and therefore Ignorance of evidence is not evidence of absence.

Even if absence of evidence really is evidence of absence, Ignorance of evidence is neither one of those things and shouldnt be mistaken for either one. Ignorance of evidence is evidence of ignorance (no, more and no less). -- BradAppleton