Quite interesting is Aristoxenus's account of what Aristotle told him about the
content of Plato's lectures on the Good. These were not in the form of Socratic
dialogues, but involved "mathematical demonstrations, including numbers,
geometrical figures and astronomy, and finally the statement Good is One". Quite
amazing!
Thomas

"It is surely better to begin by stating the nature of the inquiry, and what it
involves, so that with this foreknowledge we may proceed more easily on our
chosen way, and recognize what stage we have reached and not unwittingly deceive
ourselves about the matter. As Aristotle was wont to narrate, this was what
happened to the majority of the people who heard Plato's lecture On the Good.
Each came expecting to learn something about the things which are generally
considered good for men, such as wealth, good health, physical strength, and
altogether a kind of wonderful happiness. But when the mathematical
demonstrations came, including numbers, geometrical figures and astronomy, and
finally the statement Good is One seemed to them, I imagine, utterly unexpected
and strange; hence some belittled the matter, while others rejected it. And what
was the reason? They did not know what was coming but went along, like
argumentative people, at the mere word. But if someone begins with a summary of
his lecture, then, I hold, everyone who came to listen is free either to give
up, or, if he likes, to stay, with the understanding he has already gained.
Hence Aristotle himself, for these very reasons, as he said, used to give his
prospective audience a summary of what he intended to say, and in what manner.
Likewise it seems to me better, as I said at the beginning, to have
foreknowledge."
http://en.wikipedia.org/wiki/Aristoxenus