The fallacy of “one single proof” occurs when someone rejects overwhelming evidence because of the lack of specific evidence and declare the entire argument invalid.
A common trick of flat-Earthers is to demand unrealistic evidence of spherical Earth. After their demand is not met, they would proclaim Earth is not a sphere, and conveniently ignore all the other evidence of spherical Earth.
In many cases, such fallacious arguments are in the form of: “If X occurs or can be done, then Earth is a sphere.” Then, if the other party cannot demonstrate X, they would proclaim that Earth is not a sphere, ignoring all the other evidence of spherical Earth.
Therefore, “one single proof” can be categorized as the formal fallacy of “denying the antecedent.” If P, then Q; therefore, if not P, then not Q. Arguments of this form are logically invalid.
Usually, the “one single proof” they are demanding is unrealistic or impossible to fulfill. Even if the demands can somehow be met, they would ask for another, harder to obtain, evidence. In such cases, they would be committing the fallacy of “moving the goalposts.”
- Asking for a photo of an upside-down ship taken from a satellite.
- Demanding to see the curvature with their own eyes, without careful measurement.
- Demanding the other party to drill a tunnel to the other side of the world.
- Asking for the single credible complete undeniable irrefutable factual physical measurable evidence Earth is a sphere, then after his demand is met, he would answer by asking for the single credible complete undeniable irrefutable factual physical measurable evidence Earth is a sphere, again.