For since everything is only internal,.e., occupied with its own representations, the state of the representations of one substance could not stand in any efficacious connection at all with that of another, but some third cause influencing all of them had to make their states correspond to one another, not, to be sure, through occasional assistance specially brought about in each case (systema assistentiae),b but rather through the unity of the idea of one cause valid for all, from which, in accordance with general laws, they must all together acquire their existence and persistence, thus also their reciprocal correspondence with each other.