Currie v Misa (1875) [2] declares that consideration may comprise any of these positive and negative matters: The leading case is Stilk v Myrick (1809),[3] where a captain promised 8 crew the wages of two deserters provided the remainders completed the voyage.
The shipowner refused to honour the agreement; the court deemed the eight crew were unable to enforce the deal as they had an existing obligation to sail the ship and meet "ordinary foreseeable emergencies".
Any attempt to use promissory estoppel will fail if the debtor behaves inequitably: D&C Builders v Rees[1966][18] One party refuses to perform her side of the contract unless a larger sum of money is paid.
The rule will apply so Julian could agree to pay the extra money but then not do so when the books are delivered.
[20] The legal duty rule does not apply if the parties mutually agree to change the terms of the contract.
[21] The legal duty rule protects one party when the other is trying to change the terms of the agreement unilaterally.
[25] The restatement, however, will not always be followed, as evidenced by the decision in Labriola v. Pollard Group, Inc..[26] The pre-existing duty rule plays a part in salvage which is a "voluntary successful service to save maritime property in danger at sea".