287. [263.] Concerning simple substance, Leibniz said that his opinion regarding the monad was never like that of Wolff regarding simple substance. He said that he did indeed regard the monad as a unit, but that that unit contained within it simpler and purer substances by which the monad was formed and from which arose the changes of state in it, since if nothing were posited in it, it would be a vacuum, in which no change of state is possible, because a vacuum is incapable of being affected. Leibniz was consequently astonished that Wolff postulated his monad-which he called simple substance-to be created out of nothing, and if divided to collapse into nothing, and yet attributed to it changes of state. He was also astonished, too, that Wolff called some phenomena simple substances, including things which exist in nature, which anyone can see to be aggregates of substances, as, for example, the constituents in air and the ether, the elements in metals, and also souls. Wolff said that he hoped by the definitions of his simple substances to win over the hearts of theologians, who wish it to be believed that all things were created by God out of nothing, without any intervening means-not knowing at the time that his followers who established those principles in themselves would close to themselves the paths to angelic wisdom, which nevertheless is founded on natural truths.