Wikipedia's article on the Delphic oracle says:
The usual theory has been that the Pythia delivered oracles in a frenzied state induced by vapors rising from a chasm in the rock, and that she spoke gibberish which priests interpreted as the enigmatic prophecies preserved in Greek literature.
The idea that the Pythia spoke gibberish which was interpreted by the priests and turned into poetic iambic pentameter has been challenged by scholars such as Joseph Fontenrose and Lisa Maurizio, who argue that the ancient sources uniformly represent the Pythia speaking intelligibly, and giving prophecies in her own voice
I’m confused. If all the ancient sources say unanimously that the priestess spoke intelligibly, why does anyone believe she spoke in tongues? If they don’t say the priestess spoke intelligibly, what are Fontenrose and Maurizio talking about? Also, do historians know if the oracle generally gave straight answers, or deliberately ambiguous ones?