Now in all cases the measure of the punishment to be inflicted on the delinquent is the concurrence of the impartial spectator with the resentment of the injured. If the injury is so great as that the spectator can go along with the injured person in revenging himself by the death of the offender, this is the proper punishment, and what is to be exacted by the offended person or the magistrate in his place who acts in the character of an impartial spectator. If the spectator could not concur with the injured if his revenge led him to the death of the offender, but could go along with him if he revenged the injury by a small corporal punishment or a pecuniary fine, this is the punishment that ought here to be inflicted. In all cases a punishment appears equitable in the eyes of the rest of man kind when it is such that the spectator would concur with the offended person in exacting it. The revenge of the injured which prompts him to retaliate the injury on the offender is the real source of the punishment of crimes. That which Grotius and other writers commonly allege as the original measure of punishments, viz the consideration of the public good, will not sufficiently account for the constitution of punishments. So far, say they, as public utility requires, so far we consent to the punishment of the criminal, and that this is the natural intention of all punishments. But we still find the case to be otherwise. For though in many cases the public good may require the same degree of punishment as the just revenge of the injured, and such as the spectator would go along with, yet in those crimes which are punished chiefly from a view to the public good the punishment enacted by law and that which we can readily enter into is very different. Thus some years ago the British nation took a fancy (a very whimsical one indeed) that the wealth and strength of the nation depended entirely on the flourishing of their woolen trade, and that this could not prosper if the exportation of wool was permitted. To prevent this it was enacted that the exportation of wool should be punished with death. This exportation was no crime at all, in natural equity, and was very far from deserving so high a punishment in the eyes of the people; they therefore found that while this was the punishment they could get neither jury nor informers. No one would consent to the punishment of a thing in itself so innocent by so high a penalty. They were therefore obliged to lessen the punishment to a confiscation of goods and vessel. In the same manner the military laws punish a sentinel who falls asleep upon guard with death. This is entirely founded on the consideration of the public good; and though we may perhaps approve of the sacrificing one person for the safety of a few, yet such a punishment when it is inflicted affects us in a very different manner from that of a cruel murderer or other atrocious criminal.

Adam Smith, Lectures On Jurisprudence, ed. R.. L. Meek, D. D. Raphael and P. G. Stein, vol. V of the Glasgow Edition of the Works and Correspondence of Adam Smith (Indianapolis: Liberty Fund, 1982).