This is the
latin term for
arguing both sides of an issue and means "on either side".
Aristotle says that only by using this technique will one reach the true state of things, and that the approach is useful for anticipating counter-arguments.
This term is not so much a figure of speech as a general approach to rhetoric, or an overall argumentative strategy. It could also be used within a larger speech, though, in order to exhibit fairness to one's opponents.