duress. In Combe v Combe Denning elaborated on the equitable nature of estoppel by refusing to allow its use as a "sword" by an ex-wife to extract funds from the destitute husband. Promissory estoppel is not available when one party promises to accept a lesser sum in full payment of a debt, unless the debtor offers payment at an earlier date than was previously agreed. This is the rule formulated in Pinnel's Case, and affirmed in Foakes v Beer. This rule has, however, been thrown into doubt by the 2007 decision of Collier v Wright Ltd. Note that promissory estoppel should not be confused with estoppel for non-disclosure of knowledge, colloquially known as nolissory estoppel. This arises when a party to a contract indicates that they have some knowledge about the value or the potential success/failure of a contract to the other party, but refuses to share this knowledge or 'nol'. The party with the 'nol' is estopped from their non-disclosure and is forced to impart it equitably. Yet proprietary estoppel has also arisen by acquiescence. The leading case in this area is Ramadan v Dyson. Estoppel by acquiescence A legally binding contract occurs when one party makes an offer and receives an acceptance from the other party. A contract must consist of an offer and acceptance, the intention to create legal relations and consideration all must be present to make the contract legally enforceable. In contract law consideration is concerned with the bargain of the contract, each party to a contract must be both a promisor and a promisee. They must each receive a benefit and each suffers a detriment. The classic definition of consideration was given by the court in the case of Currie v Misa, referred to consideration as consisting of a detriment to the promisee or a benefit to the promisor, Lush J: “A valuable consideration, in the sense of the law, may consist either in some right, interest, profit or benefit accruing to one party, or some forbearance, detriment, loss or responsibility given, suffered or undertaken by the other". The doctrine of consideration can therefore be seen as a set of rules, which play the principal role in the decision by the courts as to which agreements or promises are found to be legally binding. Promissory estoppel is a term used in contract law that applies where there may not otherwise be an enforceable contract.