He parts company with Spinoza on the question of individuality.
Substance is homogeneous; but substances, or beings, are infinite.
Spinoza looked upon the universe and saw in it the undivided
background on which the objects of human consciousness are painted
as momentary pictures. Leibnitz looked and saw that background, like
the background of one of Raphael's Madonnas, instinct with
individual life, and swarming with intelligences which look out from
every point of space. Leibnitz's universe is composed of Monads,
that is, units, individual substances, or entities, having neither
extension, parts, nor figure, and, of course, indivisible. These are
"the veritable atoms of nature, the elements of things."

The Monad is unformed and imperishable; it has no natural end or
beginning. It could begin to be only by creation; it can cease to be
only by annihilation. It cannot be affected from without or changed
in its interior by any other creature. Still, it must have qualities,
without which it would not be an entity. And monads must differ one
from another, or there would be no changes in our experience; since
all that takes place in compound bodies is derived from the simples
which compose them. Moreover, the monad, though uninfluenced from
without, is changing continually; the change proceeds from an
internal principle. Every monad is subject to a multitude of
affections and relations, although without parts. This shifting state,
which represents multitude in unity, is nothing else than what we
call _Perception_, which must be carefully distinguished from
_Apperception_, or consciousness. And the action of the internal
principle which causes change in the monad, or a passing from one
perception to another, is _Appetition_. The desire does not always
attain to the perception to which it tends, but it always effects