What's it called when you use a hypothetical claim to disprove another claim?
So what I'm asking is probably niche, but it's one of those things that I'm not sure what to call it by, so apologies if the title seems off.
I think the best way to describe it is to use an example: Say in a courtroom, you (a defense attorney), assert that a witness is incorrect as even though they said they saw the defendant with greasy hands before committing murder, their fingerprints on a weapon are clean. However, the prosecutor counters by saying that the defendant could have washed their hands before they handled the weapon, aligning the witness' testimony with the evidence. While the prosecutor does not have any evidence to prove their claim, they have successfully shown potential ambiguity in the defense's own claim, derailing it.
I think the closest thing to describe this is a hypothetical, negative claim combined with absence of evidence (since negative claims don't require evidence) —but I'm not entirely positive on that and I'd like to be certain. Thanks for any help!
Both the defense and the prosecution are involved in abductive reasoning. Abductive reasoning involves reaching a plausible conclusion on the basis of what is known, even though parts of the premise or conclusion are missing (Merriam-Webster).
The defense attorney explains that the defendant had greasy hands, but the gun was clean. He takes the converse of a hypothetical (if his hands are greasy, the gun should be greasy -> if the gun is not greasy, the man who wielded it did not have greasy hands) and uses abduction to explain a likely case - the defendant's greasy hand didn't touch the gun.
The prosecutor counters with another abductive step. It is known that a hand can be wiped clean of grease. Therefore, it is also plausible that the defendant wiped his hand before touching the gun. The prosecutor used further abductive reasoning to point out that the defense attorney was affirming the consequent, or affirming the converse of a hypothetical statement without sufficiently eliminating other factors. The prosecutor's own abductive step creates a plausible case for a greasy-handed man to then wield a gun without putting grease on it:
If the man has greasy hands, the gun must be greasy. (hypothetical statement: "If A, then B")
If the gun was not greasy, the man did not have greasy hands. (converse: "If not B, then not A.")
If the gun was not greasy, perhaps the man had greasy hands but wiped them. (abductive explanation that could also fit the circumstance: "If not B, then C and A")
Abductive reasoning does not eliminate other possibilities, but rather selects on the basis of perceived probability. (Occam's razor works similarly, selecting explanations on the basis of simplicity and elegance.) Either the defense attorney or the prosecutor could be right.