Correlate to the inter-connectedness of predicates in the complete concept is an active power in the monad, which thus always acts out its predicates spontaneously. Predicates are, to use a fascinating metaphor of Leibniz’s, “folded up” within the monad. In later writings such as the Monadology, Leibniz describes this using the Aristotelian/Medieval idea of entelechy: the becoming actual or achievement of a potential. This word is derived from the idea of perfections. What becomes actual strives to finish or perfect the potential, to realize the complete concept, to unfold itself perfectly as what it is in its entirety. This active power is the essence of the monad. Leibniz has several different names for this property (or closely related properties) of monads: entelechy, active power, conatus or nisus (effort/striving, or urge/desire), primary force, internal principle of change, and even light (in “On the Principle of Indiscernibles”).