Sorrow is an emotion, feeling, or sentiment.
It is one of four interconnected sentiments in the system of Alexander Faulkner Shand, the others being fear, anger, and joy. In this system, when an impulsive tendency towards some important object is frustrated, the resultant sentiment is sorrow.
In Shand's view, the emotion of sorrow, which he classifies as a primary emotion, has two impulses: to cling to the object of sorrow, and to repair the injuries done to that object that caused the emotion in the first place. Thus the primary emotion of sorrow is the basis for the emotion of pity, which Shand describes as a fusion of sorrow and joy: sorrow at the injury done to the object of pity, and joy as an "element of sweetness" tinging that sorrow.
William McDougall disagreed with Shand's view, observing that Shand himself recognized that sorrow was itself derived from simpler elements. To support this argument, he observes that grief, at a loss, is a form of sorrow where there is no impulse to repair injury, and that therefore there are identifiable subcomponents of sorrow. He also observes that although there is an element of emotional pain in sorrow, there is no such element in pity, thus pity is not a compound made from sorrow as a simpler component.