(b) CONSIDERATION（a reward or payment for a service 报酬；酬金；支付款）. The law of contract was originally developed to meet the needs of the commercial world, and this is still reflected in the rule that only an agreement which has an element of bargain will be enforced by the courts—that is, an agreement by which each party “gives something” to the other in return for the benefit he is receiving. For example, the employer agrees to pay the price in consideration of(作为……的报酬） the contractor building the works. The benefit given—the consideration—need not be equal in any way to the benefit being received, and maybe actually doing something for the other party, or not doing something which would be to his disadvantage, or promising to do either in the future. Where one party receives no consideration of any of these kinds, an agreement will not be enforced:

The contractor may still withdraw his tender at any time because of the employer.

A contractor refused to do work unless the employer agreed to pay for it as an extra. In fact, the work was included in the contract work which the contractor was bound to do for the original contract price.

Held: The contractor gave no consideration for the employer’s promise to pay him extra, which therefore was not binding. 

A contractor submits a tender for works and agrees that it will be open for acceptance for one week has given no consideration for his promise to keep it open. But the contractor is bound by the promise if the employer makes any payment for it, however small. 

The only exception to this rule, again for historical reasons, is that a promise by a party in a document on which he has put a seal—e.g. the Agreement (p. 22)—is binding without consideration.

It follows from these principles that an employer or main contractor who requires a tender which may not be withdrawn should specify in the tender form that it is to remain open for a stated time and insist on having the tender made under seal. Another expedient is to state in the tender form that the tender will be kept open for the specified time in consideration of the employer having supplied the contract documents to the tenderer at his request. The obligation to abide by an offer may then be secured by a bid bond or cash deposit.