A contract is a promise, or set of promises, to which the law attaches legal obligation. This definition may seem somewhat unsatisfactory since it is necessary subsequently to define the circumstances under which the law does in fact attach legal obligation to promises, but in order to make a definition which should state these circumstances it would be necessary to compress the whole law of the formation of contracts into a sentence, which is impossible.' The definition given at least makes clear that the obligation of a contractor is based on a promise made by him.2

1 Many definitions of contract contain a reference to mutual assent and consideration, but these requiremente are applicable only to simple contracts.

2 It has been suggested that the conception of ft contract as necessarily involving a promise, is not accurate so far as formal contracts are contractual

It is neither the circumstances which make a promise or set of promises binding nor the legal relations between the parties which arise from the existence of a binding promise or promises which constitute the contract, but the promise or promises themselves. Though language is often loosely used, blurring these distinctions, the meaning here adopted is that of customary legal usage and probably of scientific convenience also.3