Lack of evidence is not evidence of absence, NOT!

I'll start this blog off with a bit of scientific philosophy.

“Lack of evidence is not evidence of absence.” This is one of the most commonly stated axioms in science that is obviously a fallacy yet taken as gospel in many circles. Virtually all scientists work under the assumption of its very antithesis. Bigfoot, the Loch Ness Monster, UFOs, and many other things relegated to “fringe science” and fantasy are dismissed precisely because there is a lack of sufficient evidence for most scientists to deem them credible. Scientists in typical practice do not accept hypotheses without having some evidence to lend them credence. Therefore, it follows that a lack of evidence does indeed constitute sufficient evidence of absence for most scientists to withhold support for a hypothesis. Secondly, if absence of evidence does not constitute evidence of absence, what then would qualify? If one looks for evidence to support a hypothesis and finds none, it is usually taken to mean the hypothesis is not true, until such a time that evidence turns up.
Therein lies the essential qualifier for the axiom that is commonly forgotten. Many people remember Sagan stating “lack of evidence is not evidence of absence.” Yet what is commonly neglected is the context in which the statement was made. His statement referred to the fact that until someone looked for evidence, one could not say a priori that it did not exist. However, once that task was completed, lack of evidence does indeed mean evidence of absence. Thus, more correctly, we should be saying that IF no one has looked, lack of evidence is not evidence of absence. However, IF after a thorough search and still no evidence appears, THEN we can conclude absence of evidence is indeed evidence of absence. This does not mean that at some later date evidence will not be found. It simply means that as of this point, no evidence exists to support the claim, so it is considered unfounded. It is then incumbent on those who continue to believe the hypothesis to find evidence that will convince their peers. But to simply regurgitate “lack of evidence is not evidence of absence” is intellectually disingenuous and scientifically without merit; in short, a cheat to avoid accepting the logical alternative until evidence can be found.