Absence of evidence fallacy:
|When it is argued that finding no evidence for something is no evidence for the absence of that thing.||The fact that you did not see me at your birthday party does not mean I was not there!|
This argument, attributed to Carl Sagan, is often invoked when claims of a god comes under scrutiny. While the absence of evidence is not proof of absence, it is, to varying degrees, evidence of absence. The degree of evidence an absence of evidence is for the absence of anything will depend on the context. If there is no evidence of thing X in a location Y, the degree that will constitute evidence for the absence of that thing depends upon how we substantiate the variables. Is X a molecule, mouse or monster? Is Y a cup, couch or continent? The expected discoverability of X within its relevant logical or spacial space Y must be considered.
—J.P. Moreland and W.L. Craig, Philosophical Foundations for a Christian Worldview
Case Study One
After a Harvard Medical School study on the effects of prayer on heart surgery patients showed no statistical advantage of prayer, it was wrongly argued that “the absence of evidence is not evidence of absence”.
Case Study Two
Those who claim they have the biblical Holy Spirit helping them to make predictions or avoid logical fallacies in discussion, when confronted with evidence that they are, at best, only on par with those who do not claim to have a Holy Spirit, they often invoke this absence of evidence fallacy. They then often claim the burden of proof falls on those denying the existence of their Holy Spirit.
Case Study Three
Donald Rumsfeld invoked the “absence of evidence” fallacy in reference to possible weapons of mass destruction in Iraq. Having not found WMDs where they were expected was, in fact, evidence of their absence.
Keep in mind that a fallacious argument does not entail an erroneous position.