Illegality and Public Policy
Illegality is a highly complex area of contract law. It deals with both criminal conduct, conduct prohibited by statute (even if not criminal) and conduct regarded as contrary to public policy. In some cases it will be simple to determine whether or not an illegal contract exists and will be rendered void; for example, a contract whereby A agrees to pay B $1m if B kills C will be clearly be considered illegal and void. In other cases it will be more difficult. For example, will a transport contract be rendered illegal if the car used in the transport speeds while on its journey? In some cases a contract tainted by incidental illegality might be considered unenforceable rather than void so that proprietary interests might pass notwithstanding the unlawful conduct.
Statutory illegality - this encompasses contracts directly prohibited by statute (eg, cartel contracts), contracts entered into for an illegal purpose (eg, to kill), contracts performed illegaly (eg, speeding whilst driving in the course of performing a contract) and contracts otherwise made void by statute (eg, certain unfair terms in consumer contracts). Different rules and consequences attach to each.
Common law illegality and contracts which are contrary to public policy - this encompasses a broader range of conduct, including contracts prejudicial to the administration of justice, contracts promoting corruption in public life, contracts prejudicing the status of marriage, contracts promoting sexual immorality and contracts in restraint of trade. It is not always easy to classify these types of contract and what constitutes conduct that is contrary to 'public policy' varies with the prevailing morality of the relevant jurisdiction.
Where conduct is classified as illegal or contrary to public policy it is generally held to be unenforceable; there are, however, some exceptions to that rule and, in some cases, it may be possible to sever the offending terms and enforce the remainder of the contract.