Although Leibniz was an ontological monist who believed that only one type of substance, the monad, exists in the universe, and that everything is reducible to it, he nonetheless maintained that there was an important distinction between "the mental" and "the physical" in terms of causation.
Iako je Leibniz bio ontološki monist koji je vjerovao samo jedna vrsta supstancije - monada - postoji u svemiru, i da je sve svedivo na nju, on je bez obzira držao da postoji važna razlika između «mentalnog» i «fizikalnog» u smislu uzročnosti.