Final answer:
The doctrine of innocent non est factum allows a party to recover benefits in a contract that they did not understand or intend to enter into, if the contract is found to be illegal.
Step-by-step explanation:
When one of the parties to a contract has no knowledge or any reason to know that the contract is illegal, a court may allow the party to recover benefits conferred in a partially executed contract. This concept is known as the doctrine of innocent non est factum. It is based on the principle that a person should not be bound by a contract that they did not truly understand or intend to enter into, especially if the illegality is not apparent.