etablished harmony" between the changes in one monad and those in another, which produces the
semblance of interaction. This is obviously an extension of the two clocks, which strike at the
same moment because each keeps perfect time. Leibniz has an infinite number of clocks, all
arranged by the Creator to strike at the same instant, not because they affect each other, but
because each is a perfectly accurate mechanism. To those who thought the pre-established
harmony odd, Leibniz pointed out what admirable evidence it afforded of the existence of God.
Monads form a hierarchy, in which some are superior to others in the clearness and distinctness
with which they mirror the universe. In all there is some degree of confusion in perception, but the
amount of confusion varies according to the dignity of the monad concerned. A human body is
entirely composed of monads, each of which is a soul, and each of which is immortal, but there is
one dominant monad which is what is called the soul of the man of whose body it forms part. This
monad is dominant, not only in the sense of having clearer perceptions than the others, but also in
another sense. The changes in a human body (in ordinary circumstances) happen for the sake of
the dominant monad: when my arm moves, the purpose served by the movement is in the
dominant monad, i.e., my mind, not in the monads that compose my arm. This is the truth of what
appears to common sense as the control of my will over my arm.
Space, as it appears to the senses, and as it is assumed in physics, is not real, but it has a real
counterpart, namely the arrangement of the monads in a three-dimensional order according to the
point of view from which they mirror the world. Each monad sees the world in a certain
perspective peculiar to itself; in this sense we can speak, somewhat loosely, of the monad as
having a spatial position.
Allowing ourselves this way of speaking, we can say that there is no such thing as a vacuum;
every possible point of view is filled by one actual monad, and by only one. No two monads are
exactly alike; this is Leibniz's principle of the "identity of indiscernibles."
In contrasting himself with Spinoza, Leibniz made much of the free will allowed in his system. He
had a "principle of sufficient reason," according to which nothing happens without a reason; but
when we are concerned with free agents, the reasons for their actions "incline without
necessitating." What a human being does always has a motive,