Stilk v Myrick
1809 2 Camp 317;  EWHC KB J58, 170 ER 1168
Before the start of a voyage, plaintiff contracted to work as one of 11 seaman for the voyage for $5 a month. During the voyage 2 seamen deserted; Captain then made an agreement with the rest of the crew that they should receive the wages of the deserters if they continued to work the ship back to London.
Plaintiff sued for his share of the wages of the two deserters.
(1) The agreement was not enforceable because there was no consideration given by the plaintiff for the promise to pay.
(2) The remaining crew were already bound to work the vessel back to London. The desertions were merely an emergency of the voyage and the rest of the crew remained bound by the terms of the original contract to bring the ship back to London.
(i) This case is authority for the proposition that promising or performing a duty you are already bound to the other party to perform is not good consideration for any promise he makes you.
(ii) One good reason for this rule is that it prevents contractual blackmail – where a party threatens not to perform his contractual obligations unless he gets more consideration than was originally agreed to.
See, however, the more recent cases of Williams v Roffey Bros and Musumeci.