Preexisting Duty RuleEdit
The Preexisting Duty Rule is a foundational principle of contract law that governs how modifications to an existing agreement can be enforceable. At its core, the rule says that a promise to perform a duty that one was already legally obligated to perform cannot count as valid consideration for a new promise. In practical terms, if a party already owes something under an existing contract, simply promising to do more of the same does not by itself create a legally binding modification unless there is fresh consideration or a recognized exception. This design helps preserve the reliability of bargains by preventing one side from extracting extra value by leveraging duties that were already owed.
The rule sits at the intersection of keeping promises credible and fostering a stable, predictable commercial environment. For commercial actors—creditors, suppliers, and customers alike—knowing that a modification to a contract cannot be casually bought with added promises promotes investment, planning, and risk assessment. It also reduces opportunistic bargaining that could arise if a party could demand more payment simply by reiterating an already owed duty. See the older rulings that shaped this approach in common law, particularly the English development in Stilk v. Myrick, where the court suggested that sailors who already agreed to sail could not claim extra pay by simply agreeing to take on additional work that they were already bound to perform Stilk v. Myrick.
Origins and doctrinal framing
Historical roots and the basic test: The Preexisting Duty Rule crystallized in early contract doctrine as courts wrestled with when a modification to an existing contract should be treated as a fresh agreement versus a mere reaffirmation of the original deal. The central idea is that a promise to do what one already promised to do under the first contract is not new consideration for a second contract. See the foundational discussions in many common-law courts and treatises that trace the lineage of the doctrine through cases and commentaries Stilk v. Myrick.
Restatement and modern articulation: In the United States, the Restatement (Second) of Contracts remains influential in explaining how contract modifications are evaluated. The Restatement emphasizes that modifications often require new consideration unless a recognized exception applies, or unless the modification is supported by a change in the obligations, mutual rescission, or other circumstances that justify altering the bargain Restatement (Second) of Contracts.
Exceptions and limits: There are recognized departures from the rigid preexisting duty rule. For instance, a modification can be enforceable if the parties mutually rescind the original contract and enter into a new agreement, or if there is a valid forbearance to sue that provides consideration. Additionally, in many commercial contexts, deviations from the rule occur through the operation of the Uniform Commercial Code or other statutory regimes, which address modifications in the sale of goods and related commercial transactions more flexibly. See the UCC for treatment of modifications in commercial settings Uniform Commercial Code.
The comparative angle: The doctrine has long been contrasted with doctrines of consideration and with modern doctrines like promissory estoppel, which may enforce a promise even in the absence of new consideration if one party reasonably relies on the promise to its detriment Promissory estoppel.
Core doctrine and modern practice
What counts as preexisting duty: The rule applies when a party promises to do something they are already legally obligated to do under the existing contract. The promise to perform that duty does not constitute new consideration for a modification. For example, if a contractor agrees to complete work that it has already contracted to do, the promise to perform that work for more money is typically not enforceable as a modification unless there is fresh consideration or a recognized exception Stilk v. Myrick.
How modifications are often achieved in practice: In many commercial settings, modifications are achieved by creating a new contract or by obtaining additional consideration in exchange for the revised terms. In the sale of goods or similar commercial arrangements, the UCC provides more room for changes to be recognized as binding when made in good faith, sometimes without fresh consideration, which marks a practical departure from the stricter common-law rule for non-goods contracts Uniform Commercial Code.
Alternatives to consideration: Some legal approaches rely on promissory estoppel or reliance-based theories to enforce modified promises when a party has relied on the new agreement to its detriment, even if there is no new consideration. This can be a middle path between rigidity and complete flexibility Promissory estoppel.
Controversies and debates
Pro-stability argument (center-right-friendly view): Proponents argue that the Preexisting Duty Rule helps preserve the integrity of bargains and reduces opportunistic attempts to extract more value after one party has already benefited from a duty performed. A predictable rule reduces the search for legal loopholes, lowers the cost of credit and financing, and encourages long-term planning by businesses. In this view, a robust rule discourages chisel-like tactics that could destabilize supply chains or erode trust in commercial relationships. Where modification is necessary, the preferred solution is to negotiate new terms or rely on clearly defined exceptions rather than allowing old duties to be monetized anew.
Flexibility and efficiency concerns: Critics contend that the rule can be overly rigid, especially in rapidly changing markets or during economic downturns when parties would benefit from renegotiating terms. In such contexts, requiring new consideration can stall necessary adaptations and push contracts into expensive litigation rather than constructive modification. Advocates of greater flexibility argue that good-faith modifications, mutual rescission, or reliance-based remedies may better serve efficiency and economic resilience. The UCC’s approach to goods contracts—emphasizing good faith in modifications—illustrates such practical flexibility in commercial life Uniform Commercial Code.
Woke criticisms and the critique of rigidity: From a conservative-leaning perspective in contract law, critiques that claim the rule is inherently oppressive or anti-worker are seen as overstated. They argue that the goal is not to punish business or workers but to maintain a stable baseline of obligation. When critics push for broad, unconditional flexibility in all modifications, they risk encouraging opportunism and undermining the reliability of bargains. In this view, targeted, well-justified exceptions (such as mutual rescission, unforeseen difficulties, or modifications under good faith in the sale of goods) are preferable to sweeping reforms that erode the logic of consideration. The core point is to balance fair dealing with predictable commerce, not to abandon the central assumption that promises are binding when they are backed by real, fresh consideration or legitimate alternatives to consideration.
Worked-out alternatives and policy trades: Supporters of the status quo tend to favor narrow, well-defined exceptions and the continued use of formal renegotiation processes. They argue that the law should avoid broad, redistributive policies that could distort incentives for productivity, investment, and risk management. Promissory estoppel remains a useful safety valve in cases where a party relies to its detriment on a promised modification, but it substitutes equity for the assurance of a formal contract, which is a trade-off some find undesirable in a market-oriented framework.