  Since there is a hierarchy among monads within any animal, from the soul of a person down to the infinitely small monad, the relation of domination and subordination among monads is a crucial feature of both Leibniz's idealism and his panorganicism. But the hierarchy of substances is not simply one of containment, in which one monad has an organic body which is the result of other monads, each of which has an organic body, and so on. In the case of animals (brutes and human beings), the hierarchy of monads is also related to the control of the “machine of nature” (as Leibniz had put it in a letter to De Volder considered above). What is it then that explains the relation of dominant and subordinate monads? As Leibniz tells Des Bosses, domination and subordination consists of degrees of perfection. Since monads are to be differentiated in terms of their perceptions, one natural reading would simply be that suggested in the paragraph above: monad x is dominant over monad y when x has clearer perceptions than y. But, if we follow the description of the appearance of causal interaction that we find in the Monadology (§§49–51), we can get a slightly more sophisticated picture. Monad x is dominant over monad y when x contains within it reasons for the actions of y. This is why the mind of an animal can be said to direct the actions of its body, and why, for example, there will be a hierarchy of functionality within any one animal. Thus, one's mind has clearer perceptions than those contained in the monads of its organic body, but it contains the reasons for everything that happens in one's body; one's liver contains the reasons for what happens in its cells; a cell contains the reasons for what happens in its mitochondria; and, according to Leibniz, this relation continues infinitely on down.