Certain factors affect the existence or validity of contract:
- Duress and Undue Influence: renders the contract voidable at the option of the party who was coerced or influenced, as his consent to the making of the contract was not freely given
- Incapacity: contract will be void if one party is not recognized as being capable of entering into the contract such as drunks, minors or lunatics
- Unenforceable Contracts: when a contract does not comply with required formalities
- Force Majeure: relieves the party to the contract from responsibility for non-performance or varied performance in circumstances which are entirely beyond his control.
- Void and Illegal Contracts: a contract will be void if it is a restraining a trade. A contract will be illegal if it is to perform an unlawful act.
The fact that one party to a contract acted under a mistake does not necessarily affect the validity of the contract. Contract is only void for mistake where the mistake is such that there was never any real agreement between the parties, or, if there was, if the agreement was only formed out of the same common mistake by both parties on some vital issue.