Page "Pre-established harmony" Paragraph 5

It can also be noted that if a mind behaves as a windowless monad, there is no need for any other object to exist in order to create that mind's sense perceptions, leading to a solipsistic universe consisting only of that mind.

Leibniz seems to admit this in his Discourse on Metaphysics section 14.

However, he claims that his Principle of Harmony, according to which God creates the best and most harmonious world possible, dictates that the perceptions ( internal states ) of each monad " expresses " the world in its entirety, and the world expressed by the monad actually exists.

Although Leibniz says that each monad is " windowless ," he also claims that it functions as a " mirror " of the entire created universe.