I would like to revisit these questions to show how perspective and opinions get in the way.
It has been stated that adult elephants cannot jump. We will skip varying definitions of "adult" and accept that it refers to elephants who are post-pubescent.
The statement is accepted as true, but only by consensus. People who study elephants have never seen anybody manage to get an adult elephant to jump, so it is accepted as truth. And then, it must be clarified as follows: No adult elephant can jump, if by jumping we mean the state of having no feet on the ground at the same time after propelling oneself from a stationary position.
But such a truth cannot be proven. Every single adult elephant that ever existed would have had to be tested, or the statement would have to say that no "living" elephant can jump, eliminating all past elephants from the statement since they were not tested. Even there, if an elephant could jump, it would be known that jumping is so difficult, so we would have to find some reason that each elephant would have no choice but to jump. It wouldn't be a fair test to just say "Jump" or reward any jump with a treat.
So, the statement (with clarifiers) that adult elephants cannot jump is accepted as true, although it could never really be "proven."
And it is always possible that, in the future, something that is clearly an elephant, will manage to "jump." Then this unproven truth will change. Or it can be said at that time that anything unproveable was only a theory, so this theory was "wrong" or else needed more clarifiers to make it true.
I know.... I know..... There are already some who say they have seen elephants "jump" at the circus. There will even be those that insist that their minds are not wrong, their memories are not false. Their anecdotal evidence will have to be dismissed unless credible evidence can be made available to people who study things like whether elephants can jump or not. The experts will say how those elephants were not in a stationary position or were not propelled by themself or that (most likely) the elephant lifted front legs then rear legs at separate times and never actually had all four feet off the ground at the same time. No matter how much these circus-goers insist, they will have to be accepted as "wrong", "mistaken", "tricked" or something of that sort.