Psychophysical parallelism

Psychophysical parallelism, in philosophy, is the theory that mental and bodily experiences occur in tandem with each other, but without any type of causal interaction; it denies the interaction between the body and the mind. In other words, the mind and body are two independent phenomena but cannot be separated from one another – like two sides of a coin. The theory is the third possible alternative in considering the relation between mind and body, the others being interaction and one-sided action, for example, materialism.

Occasionalism
Malebranche agreed that the mind and body were separated but did not agree with Descartes’s explanation of how the two interacted. For Malebranche, God interceded if there was a need for the mind and body to interact. For example, if the body is injured, God is aware of the injury and makes the body feel pain. Likewise, if a person wants to move their hand, i.e. to grasp an object with their fingers, that want is made aware to God and then God makes the person’s hand move. In reality, the mind and body are not actually in contact with each other, it just seems that way because God is intervening. Occasionalism can be viewed as parallelism with divine intervention so to speak, because if God did not mediate between the mind and body, there would be no interaction between the two.

Monadology
Leibniz, a German philosopher, concluded that the world was made up of an infinite number of life units called monads. A monad (from the Greek monas, meaning “single”) is similar to a living atom, and monads are all active and functioning. As there is naturally a hierarchy in nature, monads vary in degrees of intelligence. Some are more specialized and are more capable of having clearer and more distinctive thoughts opposed to monads that are simpler in structure. Next to God, humans possess the monads that are able to exhibit the highest level of comprehensive thinking. However, humans possess many types of monads, varying from very simple to very complex forms, which explains why the ideas we experience at times differ in clarity. Monads according to Leibniz can never be influenced by anything outside of themselves. Therefore, the only way that they can change, is by internal development, or more specifically, by actualizing their potential. He believed that monads never influence each other; it just seems like they do. Whenever we perceive a monad to be the cause of something, other monads are created in such a way as to seem like they are affecting the other. According to Leibniz, the entire universe was created by God to be in a preestablished harmony, so nothing in the universe actually influences anything else. Looking at psychophysical parallelism in that way, you could imagine the mind and body as two identical clocks. The clocks will always be in agreement because of the preexisting harmony between them, but will never interact. And like the two clocks, no interaction or causation among the monads that make up the mind and body is necessary because they are already synchronized.