One Mechanism, Two Valences: The English Tag Question as a Cost-Exporting Affordance

English tag questions are standardly partitioned by function, with awarm, rapport-building pole (facilitative and softening uses) opposed to aconfrontational pole (challenging, peremptory, and antagonistic uses). Thepartition obscures a structural identity: the affiliative and the coercive tagare the same grammatical mechanism, and what separates them is not form but thestakes of the proposition carried in the anchor. The shared mechanism ischaracterised here as an affordance. A declarative anchor places aspeaker-committed candidate on the floor; the appended tag formally solicitsratification or denial while leaving that candidate in place. The argument doesnot turn on whether the anchor is fully asserted: drawing on preferenceorganisation, it locates the coercion at the level of sequence rather thanpropositional commitment. The configuration exports the interactional cost ofdisagreement onto the addressee, and the same offer of an exit that renders thetag polite is what renders its coercive use deniable. A least-effort account ofthe speaker side is offered as a convergent, explicitly conjectural supplement,not as load-bearing support, and one testable prediction is derived