What made the pegasus believable?

Answer 1

The Pegasus was never believable. It was a symbol, not a creature, rather the way Uncle Sam or John Bull is a symbol. No one believes that Uncle Sam is a real person, and no one ever believed that the Pegasus was a real creature. Plato ( as "Socrates" ) betrays his unawareness of his own ignorance when he foolishly claims that his ancestors believed in centaurs ( simply the logo of the local horse-people ), medusas ( a sign like a skull-and-crossbones, meaning Stay Out!) and chimera ( merely a symbol of the three seasons in the Mediterranean year).

Plato was not alone in his ignorance: by classical times the Greeks had entirely forgotten the meaning of their own myths. Also the stories had received the Disney treatment, being reworked for literary and moral purposes, in defiance of any real meaning they may have retained.