Where a unilateral contract is broken, the only performance to be valued is that of the defendant promisor. The plaintiff ex hypothesi has already performed and is therefore entitled to the full value of the defendant's performance., The situation is the same where the contract was originally bilateral but the plaintiff has fully performed his part. Where, however, a bilateral contract is wholly or partly unperformed by the plaintiff, a distinction must be taken between the usual case of a bilateral contract with dependent promises and the exceptional case of a bilateral contract with mutually independent promises. In the former case if there has been a total breach of contract, the value of the performance promised by the plaintiff and still unperformed by him must be deducted from the value of the performance still due from the defendant.
In the exceptional case of independent promises the plaintiff's recovery will be governed by the same principles as if the defendant's promise was unilateral. There may indeed in such a case be a right of set-off, recoupment or counterclaim, but the law of damages will not adjust in an action by one party, the rights of both, except on the basis of setting off against one another two cross claims.