Each is an isolated, self-enclosed, ‘windowless’ whole. Each soul’s set of perceptions is nonetheless synchronized with all of the others, like an arrangement of movie theatres along a street, all of which play a similar movie, and where each movie contains a segment that represents what is happening simultaneously in the other movies. God, as the supreme soul and centrally controlling movie projectionist, one could say, coordinates this set of souls in a pre-established harmony. Another name for simple soul is ‘monad’, which Leibniz uses to characterize these substances, or fundamental spiritual points that constitute the universe.