Yale law professor Ian Ayres examines the pre-existing duty rule through Alaska Packers' Association v. Domenico, a case about sailors who demanded higher wages mid-voyage after already agreeing to a contract. Ayres uses the case to explain the consideration doctrine and its substitutes, asking whether a promise to pay more for work already contracted for can count as legally binding when no new consideration is given. The lecture is part of his American Contract Law course, originally built for Coursera, and walks through the court's reasoning for refusing to enforce the sailors' renegotiated pay, tying the ruling back to broader principles of contract modification and duress. Ayres works from the case file directly, breaking down the facts and the doctrinal test the court applied, making this a compact study of a foundational contracts case still taught in first-year law courses.