Monads are what the physical objects in the world, in Leibniz’s eyes, are made of. These are simple and indivisible matters, which include both physical and mental aspects, interacting with one another while existing in a pre-established God harmony. Each monad possesses a reflection of the world. They seem to fit well to the task of refuting Spinoza’s atheistic views, which Leibniz craves to do. First of all, Spinoza’s idea that people do not have any separateness from God/nature is to be challenged.
Where Spinoza sees everything as parts of one substance, Leibniz opposes monads, which in their essence are a plurality of substances. Moreover, Spinoza argues that, since people are a part of something bigger, they do not have any free will. As an answer to that, Leibniz again presents his monads, which serve as an example of substances presenting the mind which are not determined by other substances. However, it is to be noted that in avoiding casual determinism, Leibniz unexpectedly bumps into a theological one. That is, according to his views, every single thing happens to be determined by God.