Secondly: “On account of their simplicity the monads are not susceptible of alteration by another monad in their inner essence; there is no causal connection between them.” Each of them is something indifferent and independent as regards the rest, otherwise it would not be an entelechy. Each of them is so much for itself that all its determinations and modifications go on in itself alone, and no determination from without takes place. Leibnitz says: “There are three ways in which substances are connected: (1) Causality, influence; (2) The relation of assistance; (3) The relation of harmony. The relation of influence is a relation pertaining to a commonplace or popular philosophy. But as it is impossible to understand how material particles or immaterial qualities can pass from one substance into another, such a conception as this must be abandoned.” If we accept the reality of the many, there can be no transition at all; each is an ultimate and absolutely independent entity. “The system of assistance,” according to Descartes, “is something quite superfluous, a _Deus ex machina_, because continual miracles in the things of nature are assumed.” If we, like Descartes, assume independent substances, no causal nexus is conceivable; for this presupposes an influence, a bearing of the one upon the other, and in this way the other is not a substance. “Therefore there remains only harmony, a unity which is in itself or implicit. The monad is therefore simply shut up in itself, and cannot be determined by another; this other cannot be set into it. It can neither get outside itself, nor can others get inside it.”[249] That is also Spinoza’s way of regarding matters: each attribute entirely represents the essence of God for itself, extension and thought have no influence on each other.