The Purpose and Random are concepts elaborating the "grammar" of the Dark Tower universe introduced in Insomnia. The Purpose and Random are driving forces on the different levels (worlds or realities) the Dark Tower connects. There are even stronger forms like The Higher Purpose and The Higher Random. It is not totally clear whether these higher forms are multiple individual beings sharing a common aim or if they are underlying forces not bound to personal forms. Both Purpose and Random have so called agents, middle men between ordinary human beings ("Short-Timers") and the god like All-Timers. Clotho and Lachesis are agents of the Purpose, while Atropos is an agent of the Random. Central is the idea that Purpose and Random need to be in balance.
- Main article: The White
Clotho and Lachesis cut the "cords" of people whose time of living has come to an end. By cutting the cords they send the spirits of deceased "to everywhere" or "to other worlds than these". They are agents of the Purpose. The Purpose in that sense stands for order and stability.
"The Random and the Purpose are like the red and the black squares on a checker board, defining each other by contrast." - Lachesis
- Main article: The Red
Atropos is portrayed as an agent of the Random. The Random is chaos and - it seems - evil. Atropos randomly slashes people's cords which sooner or later leads to their deaths by "fulfilling circumstances". The idea is that (human) beings are designated either to the Purpose or the Random. Yet, there are certain 'undesignated" people like Ed Deepneau. When slashing his cord Atropos as agent of the Random unleashes unforeseen consequences which serve the Crimson King's plan to kill the infant Patrick Danville in order to stop Roland Deschain's path to the Dark Tower.
Higher Purpose and Higher Random
"[...] beyond the Short-Time levels of existence and the Long-Time levels on which Lachesis, Atropos and I exist, there are yet other levels. These are inhabited by creatures we could call All-Timers, beings which are either eternal or so close to it as to make no difference. Short-Timers and Long-Timers live in overlapping spheres of existence - on connected floors of the same building, if you like - ruled by the Random and the Purpose. Above these floors, inaccessible to us but very much a part of the same tower of existence, live other beings. Some of them are marvellous and wonderful; other are hideous beyond our ability to comprehend, let alone yours. These beings might be called the Higher Purpose and the Higher Random... or perhaps there is no Random beyond a certain level; we suspect that may be the case, but we have no real way of telling. We do know that it is something from one of these higher levels that has interested itself in Ed, and that something else from up there made a countermove. That countermove is you, Ralph and Louis." - Clotho