Mistake
Mistake exists where parties to a contract think that they have agreed when in actual fact they have not. For a party to be able to set a contract aside on the basis of mistake he has to establish the following. The mistake should be one of fact not law, the mistake must concern a material fact and it must be a reasonable mistake. The types of mistakes in the contract of law include unilateral mistake, mutual mistake and common mistake.

Bilateral/common mistake
This exists where both parties are mistaken .They would be thinking that they have agreed when in actual fact there is a common mistake on either side, courts have usually allowed both parties to set such a contract aside. The academic argument which is well founded is that such a contract should be treated as void because one of the requirements that is (consensus ad idem) is missing. An error on the part of both parties of a transaction regarding the same matter, such as if two people sign a contract under a certain understanding, while the contract actually conveys a different meaning than they each may have expected. That a mistake of law does not invalidate a contract was held in Ncube V Ndlovu 1985 (2) RLR 281. The appellant seduced a major daughter of the respondent. The appellant then signed an agreement undertaking to pay the respondent damages for seduction. He wanted to avoid the contract on the basis that he was mistaken as to the law that is he did not know that a father has no right to sue for damages in respect of seduction damages of a major daughter. The appeal was dismissed because this was a mistake of law not a fact.
Mutual mistake
A mutual mistake is when both parties of a contract are mistaken as to the terms. Each believe they are contracting to something different. The court usually tries to uphold such a mistake if a reasonable interpretation of the terms can be found.