Hence, secondly, the theory of "preestablished harmony" as taught by Leibnitz;--a theory which was mainly designed to explain the relation subsisting between the soul and the body, but which involves principles bearing on the general doctrine of cause and effect, and applicable to the relation subsisting between God and His works.
This theory teaches that mind and body, although closely united, have no real influence on each other, that each of them acts by its own properties and powers, and that their respective operations exactly correspond to each other by virtue of a "preestablished harmony" between the two, just as one clock may be so adjusted as to keep time with another, although each has its own moving power, and neither receives any part of its motions from the other.

This theory, therefore, denies everything like causal action between mind and matter; and when it is extended, as it may legitimately be, to the relation between God and the world, it would seem to imply the coequal existence and independence of both, and the impossibility of any causal relation between the two.

The manifest defects of these theories have given rise to a _third_, which, in one of its forms, has been generally adopted by Divines,--the theory of "instrumental causes." This theory has assumed two distinct and very different forms.

In the first, all natural effects are ascribed to powers _imparted_ to created beings, and _inherent_ in them; that is, to powers which are supposed to have been conferred at the era of Creation, and to be still sustained by God's will in Providence, subject, however, to be suspended or revoked according to His pleasure.

In the second, which resembles in some respects the doctrine of "occasional causes," all natural effects are ascribed to powers not _imparted_, but _impressed_, not belonging to the natural agent, but communicated by impulse _ab extra_; and God's will is represented as the only efficient cause in Nature.