According to the doctrine of mens rea, as we have seen, the law requires that the defendant be guilty in mind as well as in deed. The three conditions to be satisfied are that the criminal act was carried out intentionally, knowingly and of the defendant’s own free will. It is the last of these conditions that is now coming under scrutiny, and it is in many ways the most problematic of the three. The defences of necessity and duress are both complete defences, which if successful lead to acquittal. In such cases, they admit to the actus reus, but deny the mens rea. In both of them, the question of how free their action was is central to the deliberations on their guilt or innocence. We will consider the defence of duress first.