In can also frame a condition whose occurrence the speaker regards as impossible. The condition is not asserted as a genuine external possibility; rather, the argument supposes the impossible for the sake of a consequence.
This may expose the incoherence of an opponent’s claim, answer obstinacy, or reason on an adversary’s own assumptions. To hypothesize a premise is not to believe it.
The rhetoric of a counterfactual or impossible supposition is therefore distinct from the speaker’s factual commitments.