Leibniz, Monadologie
every simple substance (monad) is different from every other; every simple substance changes; therefore every monad "must include a multiplicity within a unity (or something simple). For since every natural change happens gradually, something changes and something remains. Consequently, a simple substance must contain a multiplicity of affections and relations, even though it does not contain any parts." (13)
transitory state of a monad, plurality of its properties: its perception
internal principle that brings about change: appetition [desire, appetite]
"We ourselves experience a multiplicity in a simple substance, when we find that the least thought of which we are conscious includes a variegation within its object. So anyone who accepts that the soul is a simple substance must accept this multiplicity within the monad." (16)
perceptions of monads cannot be explained through mechanistic causation (example of blowing something up, walking into it the way one walks into a mill, seeing all its parts in operation -- none of the machinery explains the being's perception) (17)