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The term "unilateral contract" is frequently used in an undesirable sense to mean that there is no contract at all, either because there has been no acceptance of the offer or because there is no consideration for the promise to be enforced. It should be used only where the agreement of the two parties has created a single duty and not mutual duties, with a single correlative right in the opposite party and not mutual rights. The term has been subjected to some criticism, a criticism that is mainly due to a failure to distinguish between physical facts, and the jural relations of persons caused by such facts. There cannot be "unilateral twins" sagely remarks Mr. Ewart, not observing that where twins exist as a fact it is quite possible for twin A to be under a duty to twin B in the absence of any duty whatever on the part of twin B to twin A.
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