In some cases, of course, full restitution is impossible. In the case of murder, for example, it is clearly impossible to restore the life taken from the immediate victim. Indeed, the life taken may be an irreplaceable value even for the survivors of the murder, who are its secondary victims. Justice, including criminal justice, is an ethics-based concept, and ethics deals only with the range of the metaphysically possiblethat is, with the choices that are available to human beings in reality (cf. "Details" box on p. 5.5:63). The concept of justice, if it is to have any practical meaning, cannot expect the impossible. Under a rational morality, the goal of criminal justice must be restitution to the fullest extent possible. The fact that an offender may not be able to repay a debt in full does not excuse him from repaying what he can to the best of his ability.
It might also be objected that some values are not merely greater than any possible repayment, but lie on a totally different scale of measurement. For example, in the instance of murder, when the aggressor cannot possibly repay his primary victim, restitution requires that payment be rendered for the value taken from the survivors of the crime. Yet it may be asked: How can we weigh the life of a loved one against a mere sum of money?