A better definition, perhaps, would make the promise a commitment that is controlled by the second party, that is, a commitment that the second party can enforce or release as he chooses. But timing is important here. The promise just discussed will work after the threat is fully committed; but if the victim of the promise (Column) can renounce the promise in advance, so that Row knows that Column expects zero if he chooses II, the threat itself is deterred. And, if the threat and promise are contrived in such a way as to be “legally” inseparable or if they are accomplished by some irreversible maneuver, the definition becomes obscured. (In fact, the definition breaks down whenever the equivalent of a promise is obtained by some irrevocable act rather than by a “legal” commitment.)

DEFINE: Distinguishes a promise from a commitment by emphasizing second-party enforcement control, while noting timing and irreversibility complicate the definition.

Thomas C. Schelling, The Strategy of Conflict, loc. 309