Volenti non fit injuria is an often-quoted form of the legal maxim formulated by the Roman jurist Ulpian which reads in original: Nulla iniuria est, quæ in volentem fiat.
Note however that comparative negligence is a partial defence, i.e. it usually leads to a reduction of payable damages rather than a full exclusion of liability.
The defence of volenti is now excluded by statute where a passenger was injured as a result of agreeing to take a lift from a drunk car driver.
Although he drove the pilot to the airfield (which was closed at the time) and helped him start the engine and tune the radio, he argued that he did not freely and voluntarily consent to the risk involved in flying.
A rescuer would not be considered volens if: An example of such a case is Haynes v. Harwood,[13] in which a policeman was able to recover damages after being injured restraining a bolting horse: he had a legal and moral duty to protect life and property and as such was not held to have been acting as a volunteer or giving willing consent to the action - it was his contractual obligation as an employee and police officer and moral necessity as a human being to do so, and not a wish to volunteer, which caused him to act.
In this case the court of appeal affirmed a judgement in favor of a policeman who had been injured in stopping some runaway horses with a van in a crowded street.
By contrast, in Cutler v. United Dairies[14] a man who was injured trying to restrain a horse was held to be volens because in that case no human life was in immediate danger and he was not under any compelling duty to act.
The court held that it would be "unseemly" to hold the doctor to have consented to the risk simply because he acted promptly and bravely in an attempt to save lives.
An example of a court reluctant to find a voluntary assumption of risk includes Carey v Lake Macquarie City Council.