A significant aspect in Leibniz's Monadology and Discourse on Metaphysics is his conception of simple substance and interaction. Leibniz assigns the term Monad to all simple substances. Monads are beings without parts, for which “neither extension, nor form, nor divisibility are possible” (M3). Monads can exist as determinate, necessary, finite, or infinite beings. For Leibniz, God exists as the one necessary and infinite Monad, which is the sole cause of the infinite determinate, independent, and finite Monads in the universe, all of which depend on God for their existence (D14). Leibniz maintained that all created Monads “have a certain perfection in themselves; there is a sort of self-sufficiency that makes them the source of their own internal actions” (M18). However, some simple substances are also endowed with the qualities of perception which is distinct from and accompanied by memory; these types of Monads are called Souls, and an example of which is the human mind (D12; M19). These finite Monads are considered independent, even if they depend on God, because each exists as a separate contained universe, which cannot interact with other finite Monads or with the external world. Interaction, defined as transposition of parts, or exchange and arrangement of matter, cannot occur between the consciousness of the Monad and the external physical world, because minds have no parts with which to interact with the extended and divisible parts of the body . Leibniz's conception of infinite simple substances and denial of mind/body interaction were developed in response to Spinoza's claim that there is only one substance and to his idea of ​​parallelism, which states that thought and extension express the same.. . of paper ......uence another.Another problem that Leibniz creates concerns his idea of ​​the necessity of God. Leibniz argues that God is necessary, but if God is necessary, then it seems that any choice that God makes in revealing these ideas innate to people must be necessary, and therefore our actions must be necessary. It seems contradictory to say that your actions are certain and determined by God, but that you don't necessarily have to follow through with those actions. It would seem that God determines your actions because those actions are the best possible choice, and since God can only choose what the best possible choice is, it would appear that God has no free will in making his decision, so all other possible actions would not even be be conceived by God because they are not possible choices, since they are not the best, and only God can choose the best.