One of the many pseudo-rationalist phrases used by apologeticists which annoy me is “Absence of evidence is not evidence of absence.” The correct formulation is ”Absence of evidence is not necessarily evidence of absence.”
It depends on the postulate. There are many many postulates which, if true, would necessarily produce checkable physical evidence.
Let’s suppose you have a neighbor who is convinced, dues to a prophetic dream, that there is a flawless diamond the size of a VW Microbus buried just about twenty five centimeters beneath the surface of her back yard.
You tell her that there has never been a diamond on the planet in history even remotely that size. She replies with equanimity that that is because her diamond is unique, and that there are things outside your knowledge.
You explain that the physical processes which create diamonds are fairly well understood, and they don’t really allow for flawless crystals that large. She shrugs and says your theories must be flawed, she knows this diamond is that big because as it happens she owns a VW Microbus.
You suggest she may have been mistaken as to the size of the diamond, and ask if she’s parked the VW Microbus beside it for comparison. She replies no, silly, the diamond is still twenty five centimeters deep in the ground, so how could she possibly park a VW Microbus under the ground?
You ask how she knows the diamond exists if she hasn’t uncovered it. She explains about the dream she had, in which an angel told her the diamond was there, and points out that angels are known for their probity.
You point out that dreams don’t always correspond to reality. She replies that she’s well aware of that, but this was a true dream about a real diamond the size of a VW Microbus in her actual backyard, because the angel assured her that was the case, and reiterates what excellent data angels provide.
Valiantly fighting off the urge to go off on a tangent that would require drawing diagrams, you suggest that given the chains of reasoning (dreams can reflect reality, that angel in her dream was an actual angel, angels don’t ever lie, and they are capable of accurately comparing the physical dimensions of VW Microbuses and improbable carbon crystals without direct observation) she might be assigning too high a confidence level to this hypothesis. She replies that her children, who are the important people in her life, have accepted the diamond wholeheartedly, that they have in fact maxed out their credit lines in the sure and certain knowledge that the diamond is there, that their lives are both more physically comfortable and emotionally tranquil as a result, and asks why you are being so hateful toward a belief that brings them comfort and joy?
I have to mention at this point how impressed I am with your patience, but all good things come to an end. Grabbing a shovel you commence digging with vigor, emitting an occasional mumbled curse as you hit rocks, all of which are however of a far lowlier status than any gemstone.
In fairly short order (i.e. that same day, finishing just before sunset) you have dug up every square foot of the yard to a depth comfortably deeper than twenty five centimeters. Turning to her you snarl triumphantly that there plainly is no such diamond there, adding perhaps that rationally the null hypothesis is that dreams are only fantasies of a tired brain and angels are similarly nonexistent lying bastards.
If she now replies that “Absence of evidence is not evidence of absence,” you might very well think you’d be justified in braining her with the shovel and burying her beside her nonexistent diamond.
You’d have my sympathy but no, alas, legally that’s not justifiable homicide.
Not even if she adds “I think I’ll plant tulips.”
