In an appeal to possibility fallacy, the speaker suggests that because something could be true that it is.
Example of appeal to possibility fallacy
Premise 1: There was a time when we couldn’t prove that something that is real actually existed.
Premise 2: We can’t right now prove that ghosts are real.
Conclusion: Ghosts are real.
Why it’s wrong
Ghosts may or may not be real, but the fact that there’s a possibility doesn’t tip the scale one way or another. The idea that there’s a possibility ghosts do exist also means there’s the possibility that ghosts don’t exist.
Put another way, I could makeup anything right now on the spot and say that it’s true simply because nobody has been able to prove me incorrect… yet.