To avoid the difficulties just stated, it is necessary to state further that "the act of exchanging the promises makes them enforceable which has been called " one of the secret paradoxes of the Common Law," 42 and thereupon also to inquire whether exchanging all mutual promises makes them enforceable, or whether this is true of only a certain kind of mutual promises and if so, what is the kind.

It makes very little ultimate difference therefore whether, conceiving that the mutual assent given in the creation of a bilateral contract is an assent to an exchange of promises in fact, one is driven to ask why all mutual promises 43 which do not contravene public policy do not make contracts (unless it is asserted that they all do) as logic would lead us to suppose; or whether the theory is accepted that a bilateral contract is based on assent to an exchange of legal obligations and in view of the impossibility of ever logically proving the existence of mutual obligations from the definition of consideration in unilateral contracts, it is asserted as a further principle that the exchange of the promises makes them enforceable and the limits of this apparent principle are sought. Whichever point of view is taken, one is turned to the cases to find what kind of mutual promises have been held by the law sufficient consideration for one another; but before doing so, the arguments

Langdell Bays the plaintiff will establish his case by proving mutual promises unless apart from consideration one of the promises is not binding, he can be justified in so asserting only if he assumes each promise by one having capacity is necessarily a detrimental obligation to the promisor, or if he assumes the mere making of a promise in fact by such a person is a sufficient detriment. The universality of his statement will not strictly be justified even if he were permitted to assume that any promise which if binding would impose a detriment is sufficient consideration, though I believe from his general argument that the last is the assumption he actually made. But certainly none of these three propositions can be accepted without proof that it represents the law. In fact all of them seem to be at variance with the law and, therefore, unsound. 4330 Law Quarterly Rev. 129, presumably by Sir Frederick Pollock. There seems nothing paradoxical about it. All that is necessary is to understand and to state that the rules governing consideration in unilateral contracts will not cover the bilateral situation, and that a special rule is re-

43 That is, all mutual promises which would be valid if under seal advanced by Professor Ames that all mutual promises not opposed to public policy create contracts should be answered.