This is best illustrated by taking a bilateral contract between A and B, where A's undertaking is conditional on B's doing what he promises to do, and where, after A has got a certain distance in his task, B breaks his half of the bargain. For instance, A is employed as a clerk by B, and is wrongfully dismissed in the middle of a quarter. In favor of A, the contract is conditional on B's keeping his agreement to employ him. Whether A insists on the condition or not, he is not bound to do any more. /1/ So far, the condition works simply by way of definition. It establishes that A has not promised to act in the case which has happened. But besides this, for which a condition [320] was not necessary, A may take his choice between two courses. In the first place, he may elect to avoid the contract. In that case the parties stand as if no contract had been made, and A, having done work for B which was understood not to be gratuitous, and for which no rate of compensation has been fixed, can recover what the jury think his services were reasonably worth. The contract no longer determines the quid pro quo. But as an alternative course A may stand by the contract if he prefers to do so, and sue B for breaking it. In that case he can recover as part of his damages pay at the contract rate for what he had done, as well as compensation for his loss of opportunity to finish it. But the points which are material for the present discussion are, that these two remedies are mutually exclusive, /1/ one supposing the contract to be relied on, the other that it is set aside, but that A's stopping work and doing no more after B's breach is equally consistent with either choice, and has in fact nothing to do with the matter. One word should be added to avoid misapprehension. When it is said that A has done all that he promised to do in the case which has happened, it is not meant that he is necessarily entitled to the same compensation as if he had done the larger amount of work. B's promise in the case supposed was to pay so much a quarter for services; and although the consideration of the promise was the promise by A to perform them, the scope of it was limited to the case of their being performed in fact. Hence A could not simply wait till the end of his term, and then recover the full amount which he would have had if the employment had continued. Nor is he any more entitled to do so from [321] the fact that it was B's fault that the services were not rendered. B's answer to any such claim is perfect. He is only liable upon a promise, and he in his turn only promised to pay in a case which has not happened. He did promise to employ, however, and for not doing that he is liable in damages.