Ancient Greek sources generally keep the Keres conceptually distinct from the Moirai, the three Fates who spin, measure and cut the thread of a person's life and thereby determine its overall length and shape. Where the Moirai governed the abstract structure of a life's duration, the Keres, and the related singular ker, were bound up specifically with the manner and moment of a violent death, particularly in battle, functioning closer to a swarm of predatory death spirits actively present at the point of dying than to the more remote, procedural Fates who set a death's timing from a distance. Walter Burkert's standard account of Greek religion notes that this distinction, while real in the literary sources, was not always sharply maintained by every ancient author, and later Greek and Roman writers occasionally blur the two categories together.
Because the Keres belong to poetic and mythological literature rather than to any documented cult with temples or regular sacrifice, they occupy a different place in the Greek religious landscape than an Olympian god or a locally worshipped hero: they are best understood as a mythic personification through which Greek epic and didactic poetry articulated ideas about the randomness, violence and inevitability of death in war, rather than as beings addressed directly in ritual practice. Their consistent association with battlefield carnage specifically, rather than death in general, marks them out among Greek death-related spirits as focused on the particular horror of dying by violence.