Argument to tradition, argument from antiquity
Fallacious arguments to tradition assert that a belief is correct solely because the belief is ancient or is supported by tradition. This fallacy is the reverse of an equally fallacious argumentum ad novitatem (argument for novelty).
It is certainly true that some reasonable beliefs have persisted through time, yet old beliefs must be assessed on their merits, and not on their longevity alone. There may be extenuating circumstances that explain the persistence of an unfounded ancient belief. Such a belief may persist because it has emotional appeal or because it is a key element in a system of belief that has both emotional appeal and organizational support.
The Greeks believed that the sun was pulled across the sky by a horse-drawn chariot, yet a person insisting upon such an idea today would be widely regarded as certifiable. The old Greek idea was abandoned long ago partly because scientific awareness intervened, but also because other religious belief systems supplanted Greek mythology.
Because Christian belief has persisted to this day for historical reasons, Christians fail to see that they commit this fallacy whenever they argue that long-standing belief that Christ was the Son of God ensures that Christ was indeed the Son of God. In fact, some would also erroneously argue that the fact that the Son of God story has persisted, while the Sun Chariot myth disappeared, indicates that Christ was indeed the Son of God. Such an argument is a false dichotomy because it ignores more likely explanations for the persistence of the Son of God myth. (The false dichotomy, in the mind of many Christians runs, "either you acknowledge that Jesus was the son of God or you are incorrect.")
The Greek myth held that the sun was the god Helius (later Apollo) who was a son of the Titans Hyperion and Theia. Helius was the brother of the goddesses Selene (the moon) and Eos (the dawn). In early versions, bulls drew Helius' chariot, whereas the horses Pyrois, Aeos, Aethon, and Phlegon drew the chariot in later mythology. (Perhaps the bulls quit!).
(The image is a modified section of this painting.)