The Greek term μονάς, from which the word monad is derived, means a "unit" or a "one." In Pythagorean writings it is the unity from which the entire number system, and therefore—as a consequence of the doctrine that "everything is number"—all things, are derived. Through Plato, who applied the Pythagorean term to the Ideas or Forms (Philebus V, 15B), it entered the tradition of Neoplatonism and Christian Platonism to mean a simple, irreducible, self-determining entity whose activity is the source of all composite beings. In this sense it was sometimes used to designate God as the simple source of all being and sometimes to signify the simplest irreducible entities in the created order out of whose harmonious action all existence is compounded.

A monadology is a metaphysical system that interprets the world as a harmonious unity encompassing a plurality of such self-determining simple...