Mistakes can affect the validity of contracts in different ways depending on whether the mistake was common to both parties, unilateral, or mutual. [1] For a common mistake, the contract will usually be void if the subject matter does not exist or belongs to one party already. [2] For a unilateral mistake, the contract may be void if the mistaken party did not understand the contract terms and the other party was aware, while for identity mistakes additional conditions must be met depending on if parties were present. [3] For a mutual mistake where the parties misunderstood each other, the contract could be void if an objective reasonable person would not understand it in only one sense.