Jeremy,
"Accurately describes reality".
“Accurately” according to what metrics? Lots of things have been thought to be accurate descriptions of reality that have turned out to be no such thing. The most we can say is something like, “most congruent with the methods and tools available at this time to determine provisional accuracy”.
But if there is no volcano god, the islander is wrong and his belief is a falsehood.
And if the moon doesn’t orbit the Earth then we are wrong and our belief about that is false too. That’s the point – things are only as true as we can establish them to be, but no more.
The fact that you can never be 100% certain of the truth does not alter the fact that "the Moon orbits the Earth" is either true or it isn't. You may be absolutely certain that the Moon orbits the Earth and 99% of the population may be certain that the Moon orbits the Earth but it does not alter the fact that the Moon does not orbit the Earth and your belief is false.
Sort of, but the idea of “100% true” is a philosophical problem rather than an evidential one. Even if we thought we had every possible piece of evidence there ever could be for a conclusion, we have no means to eliminate the possibility at least of an unknown unknown that could show us to be wrong. That something “either is true or it isn’t” is fine conceptually, but that’s all it is.
This "true for me" stuff really annoys me because it allows people to avoid dealing with reality. It lets the believers of nonsense off the hook. Why can't we just be honest and say "the Moon orbits the Earth is a simplification of the fact that the Moon orbits the centre of mass of the Earth-Moon system and even that is also a simplification because you have to add in the effects of the Sun, planets and other mass in the Universe".
I don’t think it need let them off the hook at all. If Fred says, “the moon orbits the Earth” and Jill says, “the Earth orbits the moon” Fred's claim can be shown probabilistically to be more likely to be true than Jill's within the context of the tools available to both Fred and Jill. And that’s enough for Fred’s claim to be accepted and Jill’s to be dismissed. The danger though is in Fred overreaching into claiming certainty for his truth.