Psychophysical parallelism
In the philosophy of mind, psychophysical parallelism is the theory that mental and bodily events are perfectly coordinated, without any causal interaction between them. As such, it affirms the correlation of mental and bodily events, but denies a direct cause and effect relation between mind and body. This coordination of mental and bodily events has been postulated to occur either in advance by means of God or at the time of the event or, finally, according to Baruch Spinoza's Ethics, mind and matter are two of infinite attributes of the only Substance-God, which go as one without interacting with each other. On this view, mental and bodily phenomena are independent yet inseparable, like two sides of a coin.
Overview
Psychophysical parallelism is a third possible alternative regarding the relation between mind and body, between interaction and one-way body-to-mind causality.Parallelism is a theory which is related to dualism and which suggests that although there is a correlation between mental and physical events there is not any causal relationship. The body and mind do not interact with each other but simply operate independently of each other, in parallel, and there happens to be a correspondence between the two but neither causes the other. That is to say that the physical event of burning your finger and the mental event of feeling pain happen to occur simultaneously as a response to contact with a hot object—one does not cause the other.
In his 1925 book The Mind and its Place in Nature, C. D. Broad maintains concerning parallelism: "The assertion is that to every particular change in the mind there corresponds a certain change in the brain which this mind animates, and that to every change in the brain there corresponds a certain change in the mind which animates this brain."
Relation to other philosophies
Psychophysical parallelism v. epiphenomenalism
Psychophysical parallelism can be compared to epiphenomenalism due to the fact that they are both non-fundamentalist methods to link mind and body causality. Psychophysical parallelism is the ideology that the mind and the body hold no interaction between them, but that they are synchronized. On the other hand, epiphenomenalism proclaims that mental occurrences can be triggered by physical ones, but that mental occurrences do not affect anything, they simply spark and fade, so they do not cause any events whatsoever. For instance, let’s picture one accidentally cutting themself while chopping avocados. From the view of psychophysical parallelism, the physical neural reaction would not provoke the mental state of pain itself, rather pain would be triggered in coordination with the physical reaction. And so, the mind and the body do not affect each other. However, from the perspective of epiphenomenalism, the mental states of pain would be occasioned by the physical event of the neural reaction of cutting through the skin. The mental states of pain then irritation or sadness will occur and pass one after the other. Ultimately, the difference lies in the belief of correlation between mental and physical, which epiphenomenalism believes present, while parallelism does not.Relation to causal closure
Causal closure is the metaphysical theory which dictates that every process stems from a cause and expresses consequences of its respective nature.. This implies that the mental and physical processes do not affect each other, as they cannot interact with one another.Causal closure iterating that the physical and mental world cannot interact presents an obvious issue in regard to dualism. In the world of dualism, the mind and body are two entirely separate constituents which continuously interact with each other, in order for the human being to function as a whole. Causation therefore fundamentally discredits dualism.
Psychophysical parallelism accordingly provides a solution for dualists. Psychophysical parallelism explains that the mental mind and the physical body undergo the same experiences in a parallel fashion. Ergo, they do not interact with one another, but they act and react cohesively and simultaneously. This theory offers an explanation on behalf of dualism : the mind and body remain two distinct properties of humans, yet they do not interact with each other. They rather function in parallel to each other : coordinated but independent.