34 HARVARD LAW REVIEW. down the general rule. that doing what one is bound to do is not a good consideration, but apply it to this class of cases, therefore carry out to its logical conclusion the doctrine of consideration, in making the test what the promisee has given, not what the promisor has received. Conceding most of this argument, an attempt has been made by some to distinguish unilateral and bilateral agreements. In Professor Langdell's Summary of the Law of Contracts,^ it is said : "It will sometimes happen that a promise to do a thing will be a sufficient consideration when actually doing it would not be. Thus, mutual promises will be binding though the promise on one side be -merely to do a thing which the promisee is already bound to a third person to do, and the actual doing of which would not, therefore, be a sufficient consideration. The reason of this distinction is, that a person does not, in legal contemplation, incur any detriment by do- ing a thing which he was previously bound to do, but he does incur a detriment by giving another person the right to compel him to do it, or the right to recover damages against him for not doing it. One obligation is a less burden than two (i. e. one to each of two per- sons), though each be to do the same thing." The same distinction is also involved in the discussion of the subject by Sir Frederick Pollock, in the first edition of his treatise on the law of contracts.^ Sir William Anson, however, pointed out a fallacy in this line of reasoning,^ in that it assumes that the second promise does impose an obligation upon the promisor. As both parties to a bilateral contract are bound or neither is bound, this assumption involves the further assumption that the second promise is itself a sufficient consideration to support the counter-promise, — the very point in dispute. Anson then suggests another line of reasoning to sus- tain the second agreement.* " The case may however be put in this way ; that an executory contract may always be discharged by agreement between the parties ; that A and M, parties to such an agreement, may thus put an end to it at any time by mutual consent ; that if X says to A, ' Do not exercise this power, insist on the performance by M of his agreement with you, and I will give you so and so,' the carrying out by A of his agreement, or his promise to do so, would be a consideration for a promise by X. A in fact agrees to abandon a right which he might have exer- cised in concurrence with M, and this, as we have seen, has always 1 Sect. 84. 8 Anson, Contracts (ist ed.), 8a 3 Pollock, Contracts (ist ed), 158. * Page 81.
