Parties frequently agree to change their bargain mid-performance, yet a promise to pay more or accept less is often worth nothing in law. This chapter begins with the nature and form of a variation, including whether a 'no oral modification' clause can shut out informal changes, before tackling the consideration problem: when performing an existing duty counts as good consideration, the practical benefit doctrine, and the stubborn rule against part payment of a debt with its exceptions. It then examines how economic duress can unravel a variation extracted under pressure, and how promissory estoppel may hold a party to a promise even without consideration. It closes by separating variation from the related concepts of waiver and novation.
