for self-interest). God and the good angels therefore have free will despite being incapable of sinning; similarly, the non-coercive aspect of free will enabled man and the rebel angels to sin, despite this not being a necessary element of free will itself. In , Anselm further considers the case of the fallen angels, which serves to discuss the case of rational agents in general. The teacher argues that there are two forms of good—justice () and benefit ()—and two forms of evil: injustice and harm (). All rational beings seek benefit and shun harm on their own account but independent choice permits them to abandon bounds imposed by justice. Some angels chose their own happiness in preference to justice and were punished by God for their injustice with less happiness. The angels who upheld justice were rewarded with such happiness that they are now incapable of sin, there being no happiness left for them to seek in opposition to the bounds of justice. Humans, meanwhile, retain the theoretical capacity to will justly but, owing to the Fall, they are incapable of doing so in practice except by divine grace. Cur Deus Homo ("Why God was a Man") was written from 1095 to 1098 once Anselm was already archbishop of Canterbury as a response for requests to discuss the Incarnation. It takes the form of a dialogue between Anselm and Boso, one of his students. Its core is a purely rational argument for the necessity of the Christian mystery of atonement, the belief that Jesus's crucifixion was necessary to atone for mankind's sin. Anselm argues that, owing to the Fall and mankind's fallen nature ever since, humanity has offended God. Divine justice demands restitution for sin but human beings are incapable of providing it, as all the actions of men are already obligated to the furtherance of God's glory. Further, God's infinite justice demands infinite restitution for the impairment of his infinite dignity. The enormity of the offence led Anselm to reject personal acts of atonement, even Peter Damian's flagellation, as inadequate and ultimately vain. Instead, full recompense could only be made by God, which His infinite mercy inclines Him to provide. Atonement for humanity, however, could only be made through the figure of Jesus, as a sinless being both fully divine and fully human. Taking it upon himself to offer his own life on our behalf, his crucifixion accrues infinite