Psychophysical parallelism

Psychophysical parallelism (or parallelism) is the philosophical theory that mental and bodily events occur together, without any causal interaction between them. As such, it affirms the correlation of mental and bodily events, but denies any causal relationship. On this view, mental and bodily phenomena are independent but inseparable– like two sides of a coin. The theory is a third possible alternative of relation between mind and body, between interaction (eg, dualism) and one-sided action (eg, materialism or epiphenomenalism).

A prominent version of parallelism is called occasionalism. Defended by Malebranche, occasionalism agrees that the mind and body are separated but does not agree with Descartes’s explanation of how the two interacted. For Malebranche, God intercedes 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.

According to Baruch Spinoza, as explicated in his Ethics, the two attributes of God of which we have cognizance, namely Thought and Extension, are not causally related. Rather, they are two different ways of comprehending one and the same reality. Thus, the human body has a corresponding idea, which is the human mind or soul. Whatever happens in the body always occurs in tandem with contents of the mind. Since everything that exists is a modus of God, Spinoza's concept represents a monist account of parallelism, contrary to Leibniz's pluralist version.

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