'Promissory estoppel' may allow enforcement of a promise, even without traditional consideration, when:

解析

Promissory estoppel substitutes detrimental reliance for bargained-for consideration: the promisor should reasonably expect the promise to induce action or forbearance, the promisee does justifiably and substantially rely, and injustice can be avoided only by enforcing the promise. In construction the classic application is a general contractor's reliance on a subcontractor's bid — Drennan v. Star Paving (1958) 51 Cal.2d 409. Each distractor removes one required element: (b) drops foreseeability of reliance, so the promisor had no reason to guard his words; (c) drops reliance itself, leaving a bare gratuitous promise that no theory enforces; (a) drops the objective reasonableness that makes reliance justifiable.