However, somewhere rather late in sub-human psychism revengeful emotion certainly arose as an advantageous variation, and it grew in strength and prominence for many ages of psychic progress. At length it culminated, and began its decline with the marked increase of co-operative sociality, with which it must greatly interfere. Reprisal and counter-reprisal, vendetta, feud, is opposed to that social union which is strength; and so we see that tribes and nations in which the spirit of personal revenge has been a dominant trait have been left behind in the march of progress. Revengefulness, at least in the form of retributive personal violence for injuries done, is, in a highly civilized community, entirely superseded by the machinery of law. Instead of slaying a brother’s murderer I call upon the law to execute justice and retribution, and I bring certain designated ones among my fellows to secure my revenge. Where a man takes the law in his own hands, and kills or injures the violator of his home or the slayer of his nearest kin, he recedes to the lower unsocial plane from which civilization has arisen. Thus revengefulness, in certain forms at least, has become in the highest human communities a disadvantageous variation, and is gradually being eliminated. This negative elimination of revenge is also greatly hastened by the progress of certain ethical and Christian conceptions by which a new and opposite law of conduct is enforced, namely, the returning good for evil. One of the most interesting and most retrospective of emotions is sorrow. Sorrow, grief and regret are wholly regardful of the past, are pains at the past. They are purely subjective or “mental” pains at the past, and in no wise pains from the past; they are not pains recurrent from past pains, but purely a painful emotion at the representation of past pain. Thus, a man says, “I did it to my own harm and hurt, and I have always been sorry I did it.” Here the sorrow-pain is evidently quite distinct from the direct pain of the injury; pain for the harm done is one thing, and pain from the harm done is another. I hurt myself, and I not only have this pain, but, being sorry that I did it, I have this new emotional pain added. Sorrow as painful emotion for the past is thus plainly unique and peculiar. To feel sorry over what has happened is a mode of feeling altogether different from feeling proud of it, angry at it, etc., and we may reasonably regard sorrow as a distinct _genus_ of retrospective emotion. What, now, is the nature and function of this special emotion reaction?