We are thus introduced, from a new point of view and in a more concrete way, to the conception of pre-established harmony. The activity of one, the energy which gives the law to the other and makes it subordinate in the hierarchy of monads, is conceived necessarily as spirit, as soul; that which receives, which is rendered subordinate by the activity of the other, is body. The pre-established harmony is the fact that they are so related that one can receive the law of its activity from the other. Leibniz is without doubt partially responsible for the ordinary misconception of his views upon this point by reason of the illustration which he was accustomed to use; namely, of two clocks so constructed that without any subsequent regulation each always kept perfect time with the other,--as much so as if there were some actual physical connection between them. This seems to put soul and body, spirit and matter, as two co-ordinate substances, on the same level, with such natural opposition between them that some external harmony must arrange some unity of action. In causing this common idea of his theory of pre-established harmony, Leibniz has paid the penalty for attempting to do what he often reproves in others,--imagining or presenting in sensible form what can only be thought. But his other explanations show clearly enough that the pre-established harmony expresses, not a relation between two parallel substances, but a condition of dependence of lower forms of activity upon the higher for the law of their existence and activity,--in modern terms, it expresses the fact that phenomena are conditioned upon noumena; that material facts get their significance and share of reality through their relation to spirit.