The story goes that CORAX, the first teacher of rhetoric in ancient Greece, had a pupil named Tisias. when it came time for Tisias to pay Corax his fee, Tisias refused, and Corax took him to court to get the money out of him. (In ancient Greece, you typically presented your own case in court.) Tisias -- ever the star pupil -- argued that either [a] he shouldn't have to pay, because Corax had failed to teach him rhetoric effectively, or [b] if Corax had indeed taught him effectively, this presentation to the jury would be persuasive -- so that either way he shouldn't have to pay. Corax argued the opposite.
The jury deliberated briefly over the case, and then threw them both out of court, quoting the proverb, A BAD EGG FROM A BAD CROW ('corax' is also the ancient Greek word for 'crow'). Our proverb, 'The apple doesn't fall very far from the tree,' has a similar sense.
For more on Corax and the origins of rhetoric, interested readers may consult the following:
George A. Kennedy, A New History of Classical Rhetoric, Princeton University Press 1994;
Edward Schiappa, The Beginnings of Rhetorical Theory in Ancient Greece, Yale University Press 1999;
-- and -- for a fascinating speculative inquiry -- see
Thomas A. Cole, "Who Was Corax?," Illinois Classical Studies 16 (1991) 65-84