Absence of Evidence is not Evidence of Absence ... or is it?

“Absence of evidence is not evidence of absence”, is a saying frequently quoted by cryptid proponents, more especially Bigfoot proponents, in an attempt to dismiss the fact that no type specimens have ever been found. Ironically, most of those who employ this saying do not realize that they are quoting a skeptic that did not believe in Bigfoot, or alien animals, or prehistoric survivors, or any of the other popular figures of cryptozoology.

The quote can be found on page 213 of Carl Sagan’s, “The Demon-Haunted World—Science as a Candle in the Dark”, and is strictly used to criticize “argumentum ad ignorantiam (“appeal to ignorance”), which is to say that “something must be true because it cannot be proven false, and vice versa”.

I do not entirely agree with Carl Sagan’s quote. In my opinion, absence of evidence can only be evidence of absence. Missing evidence is, after all, a very clear indication that the evidence is probably not there. However, I realize that absence of evidence is not proof of absence. But if Dr. Sagan had stated it that way, then we would not have a nifty little, easily memorized antimetabole that, despite my disagreement, conveys an apparent truth in the proper context.

Contrary to many proponents, I believe that cryptozoology falls short of the proper context, and I believe that Dr. Sagan agrees. On page 171 of the above quoted book, Dr. Sagan introduces us to the invisible dragon in his garage; a dragon that is impervious to the five senses. After introducing us to his undetectable dragon, he states, “What I’m asking you to do comes down to believing, in the absence of evidence, on my say-so”, which is to say, believing the undetectable dragon is evident, despite the absence of evidence. The point Dr. Sagan is making is that we should not accept “say-so” without the support of empirical evidence. In other words, in this case, the “absence of evidence” is indeed “the evidence of absence”.

Bigfoot and the other popular cryptids largely fit the criteria of Dr. Sagan’s undetectable garage dragon. After using his invisible dragon to show us the inefficacy and unreliability of “say-so”, Dr. Sagan writes, “The only thing you’ve really learned from my insistence that there’s a dragon in my garage is that something funny is going on inside my head.”

Granted, a garage is a tad smaller and easier to go through than thousands of square miles of forest and woodland. But I must nevertheless ask; is something funny going on inside someone’s head when they expect everyone to unquestionably believe that the existence of Bigfoot, or any other unlikely cryptid, is absolute; especially when it appears to be just as invisible and undetectable as Dr. Sagan’s hypothetical garage dragon?

Sadly, Carl Sagan is no longer with us to clarify his quote, but it is my opinion that Dr. Sagan logically believed that absence of evidence can indeed be evidence of absence.

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