Consideration: the price of an enforceable promise

Suppose a wealthy uncle promises his niece five thousand dollars for her birthday, and then changes his mind. Morally, the broken promise is blameworthy; legally, in common law systems, the niece has no claim. The reason lies in the doctrine of consideration, the rule that a promise is enforceable only if the promisee has given, or promised to give, something in exchange for it. Consideration is the price of admission to the law of contract.

The doctrine performs several functions at once. Evidentially, an exchange is easier to prove than a bare declaration of generosity. Cautionarily, the act of giving something signals that the promisor's commitment was deliberate. And economically, the doctrine channels legal enforcement toward bargains — the reciprocal transfers on which markets run — rather than toward one-way gifts, which civil law systems treat more generously.

Consideration need not be money. It can be an act, a forbearance, or a counter-promise. What matters is that the law sees a bargain: each side's promise or performance is the inducement for the other's.

Sufficient but not adequate

Courts insist that consideration be real, but they refuse to appraise it. A peppercorn rent can support a lease; a trivial sum can buy a valuable option. The classic formula is that consideration must be sufficient — recognized by law as having value — but need not be adequate — equal in value to what is received. This hands-off posture reflects the liberal premise that competent adults are the best judges of their own interests, and that judicial price-fixing would chill trade.

There are limits. A promise to perform a duty the promisor already owes — to refrain from a crime, or to fulfill an existing contract with the same party — is ordinarily illusory as consideration, because the promisor has given nothing new. Yet where performance of an existing duty confers a practical benefit, such as keeping a construction project on schedule, modern courts have sometimes found consideration in the benefit itself.

Past acts and moral obligations

Because consideration must be the price of the promise, acts done before the promise was made cannot support it. If a passerby rescues a drowning swimmer and the grateful swimmer later promises a reward, the rescue cannot be the consideration: it was never bargained for. A narrow exception exists where the act was done at the promisor's request, in circumstances implying that payment was always expected, as when a professional performs services later confirmed by a promise to pay.

Neither does moral obligation suffice. A debt barred by a limitation period, or a promise made out of gratitude, cannot be revived by conscience alone. The law's insistence on bargain keeps the boundary between legal duty and moral sentiment clear, even where that boundary feels harsh.

Estoppel and the deed

Two escape routes soften the doctrine's rigor. The first is the deed: a promise executed in a formal written instrument, signed and witnessed, is binding without consideration, a survival of the medieval seal. The second is promissory estoppel, an equitable doctrine that prevents a promisor from retracting a promise which the promisee has foreseeably and detrimentally relied upon. Estoppel is usually a shield rather than a sword — it defends, but rarely creates, a cause of action.

Together these doctrines sketch the common law's considered position: bargains bind, gifts do not, except where formality or reliance supplies what bargain lacks. This overview is educational and not legal advice.