It is no consideration for a promise for a man to forbear or to promise to forbear from doing what he is not legally entitled to do.91 This proposition would seem to be obvious, but questions have arisen in its application, and have given rise to some conflict in the decisions.
Some applications of the principle are clear. A forbearance or promise to forbear, for instance, from claims under an illegal contract, such as a gambling contract, or a contract involving the commission of crime, can form no consideration for the promise of the other party, since the contract is void, and could not be enforced.92 So, also, the release of a debtor from imprisonment was held to be no consideration for a promise where, by the previous release of a codebtor, the debt had been discharged, since the imprisonment was therefore unlawful.98 So a promise to pay rent, made solely to prevent an unlawful eviction, is without consideration.94
As a general rule, it is safe to say that, in order that forbearance to exercise a right may constitute a consideration, the right must be at least doubtful. Forbearance to insist upon a claim that is clearly unenforceable, at least if it be known to the claimant to be such, cannot be a consideration.