If someone is accused of breach of contract, there are a number of defenses available to argue that a contract should not be enforced. If any of the basic contract elements are missing, or if the contract was made with someone of diminished capacity or for illegal purposes, a contract can be unenforceable. Some other examples of potential defenses to enforcement of a contract are mutual or unilateral mistake, duress or undue influence, unconscionability, misrepresentation or fraud, impossibility or impracticability, and frustration of purpose.
Mutual or Unilateral Mistake
There are two types of mistakes in contract law: mutual mistake and unilateral mistake. When there is mutual mistake, both parties have made a mistake regarding the contract and there is generally an issue of whether the parties actually reached a meeting of the minds. In such situations, there is a question of whether a contract even exists. If the mistake significantly changed the subject matter or the purpose of the contract, the court will not enforce it.
Unilateral mistake is when only one party is mistaken regarding the contract. Usually, unilateral mistake is not a basis for voiding a contract. However, if one party caused other's mistake, or knew the other party was mistaken and did nothing to correct it, the court will probably not enforce the contract.
Duress or Undue Influence
Duress occurs when one party is forced to enter into a contract that he would not have entered voluntarily. Blackmail, threats of physical harm, or threats of legal proceedings can all be forms of duress that will cause a court to find that a contract is not binding.
Undue influence is similar to duress but does not usually involve conduct that is so severe. Undue influence occurs when someone exercises such control over another person that the influencer’s will is substituted for that of the controlled person. Simple persuasion does not constitute the kind of