Interactionism or interactionist dualism is the theory in the philosophy of mind which holds that matter and mind are two distinct and independent substances that exert causal effects on one another. An example of your mind influencing your body would be if you are depressed (which is related to your mind), you can observe the effects on your body, such as a slouched posture, a lackluster smile, etc. Another example, this time of your body affecting your mind would be: If you struck your toe very forcefully on a door (which is related to your body), you would experience terrible pain (which is related to your mind). Interactionism is one type of dualism, traditionally a type of substance dualism though more recently also sometimes a form of property dualism. Many philosophers and scientists have responded to this theory with arguments both supporting and opposing its relevance to life and whether the theory corresponds to reality.
Proponents
René Descartes Interactionism was propounded by the French rationalist philosopher René Descartes (1596–1650), and continues to be associated with him. Descartes posited that the body, being physical matter, was characterized by spatial extension but not by thought and feeling, while the mind, being a separate substance, had no spatial extension but could think and feel. Nevertheless, he maintained that the two interacted with one another, suggesting that this interaction occurred in the pineal gland of the brain.
Development of interactionism In the 20th century, its most significant defenders have been the noted philosopher of science Karl Popper and the neurophysiologist John Carew Eccles. Popper, in fact, divided reality into three "worlds"—the physical, the mental, and objective knowledge (outside the mind)—all of which interact,Three Worlds by Karl Popper – The Tanner Lecture on Human Values – Delivered by Karl Popper at The University of Michigan on April 7, 1978. and Eccles adopted this same "trialist" form of interactionism. Other notable recent philosophers to take an interactionist stance have been Richard Swinburne, John Foster, David Hodgson, and Wilfrid Sellars, in addition to the physicist Henry Stapp.
Avshalom Elitzur has described himself as a "reluctant dualist". One argument Elitzur makes in favor of dualism is an argument from bafflement. According to Elitzur, a conscious being can conceive of a P-zombie version of his/herself. However, a P-zombie cannot conceive of a version of itself that lacks corresponding qualia.
In his 1996 book The Conscious Mind, David Chalmers questioned interactionism. In 2002 he listed it along with epiphenomenalism and what he calls "Type-F Monism" as a position worth examining. Rather than invoking two distinct substances, he defines interactionism as the view that "microphysics is not causally closed, and that phenomenal properties play a causal role in affecting the physical world." (See property dualism.) He argues the most plausible place for consciousness to impact physics is the collapse of the wave function in quantum mechanics.
The New Catholic Encyclopedia argues that a non-physical mind and mind–body interaction follow necessarily from the Catholic doctrines of the soul and free will.Maher, Michael (1909) "The Law of Conservation of Energy", Catholic Encyclopedia, vol. 5, pp. 422 ff, https://www.newadvent.org/cathen/05422a.htm.
Objections Problem of causal interaction
Today the problem of causal interaction is frequently viewed as a conclusive argument against interactionism. On the other hand, it has been suggested that given many disciplines deal with things they do not entirely understand, dualists not entirely understanding the mechanism of mind–body interaction need not be seen as definitive refutation. The idea that causation necessarily depends on push-pull mechanisms (which would not be possible for a substance that did not occupy space) is also arguably based on obsolete conceptions of physics.
Objection from Princess Elizabeth of Bohemia One objection often posed to interactionism is the problem of causal interaction – how the two different substances the theory posits, the mental and the physical, can exert an impact on one another. This objection was initially made by Elisabeth, Princess of Bohemia and is known as Princess Elisabeth's objection. She questions how an immaterial substance (mind) can interact with a material substance (body) given that they cannot make physical contact. An example of a physical-physical interaction is how when a cue ball hits another billiards ball, it causes it to move. Princess Elisabeth questioned how a mental occurrence, such as intention, can cause a finger to move if immaterial things never come into direct contact with the physical world.
Elizabeth of Bohemia's objection is part of the "pairing problem", a point raised by the philosopher Jaegwon Kim that Amy Kind also mentions in her book. The pairing problem objects the Cartesian dualism more particularly interactionism by questioning the possibility of the interaction of immaterial things such as the mind with material things such as the body by showing the difficulty of doing so. The argument that Jaegwon Kim presents supporting the pairing problem says that it is not possible to give a causal explanation to an event between two immaterial entities or an event between an immaterial and a physical entity. As a response to Elizabeth of Bohemia's objections, Descartes asserts that the mind–body relationship is misunderstood. As a counterargument to his critics, he drew an analogy between the mind and gravity, stating that if gravity can have an effect on a material body without physical contact, then the mind can also have an effect on the body. Elizabeth of Bohemia found Descartes's response unsatisfactory because, according to her, the analogy of gravitation explains what occurs between mind and body but does not help us understand how immaterial entities interact with material entities. Elizabeth of Bohemia finds that Descartes's explanations does not explain how the mind associates itself with the body in order to be able to do things such as physical movements of particular body parts. Eventually, after a few correspondences, Descartes's response became more evasive and was deviated on other topics such as the Princess's misconceptions and her health. Despite the fact that Elizabeth of Bohemia is remembered as a critic of René Descartes, she agrees with him on a few points, such as the principle of interactionism meaning the fact that the mind and body can influence each other. In addition to that, she appreciates his reasoning and believes she can learn and expand her knowledge from it.
Occasionalism Descartes' theory that interaction between the mind and the physical world occurred in the pineal gland was seen as inadequate by a number of philosophers in his era, who offered alternate views: Nicholas Malebranche suggested occasionalism, according to which mind and body appear to interact but are in fact moved separately by God, while Gottfried Leibniz argued in The Monadology that mind and body are in a pre-established harmony. On the other hand, Baruch Spinoza rejected Descartes' dualism and proposed that mind and matter were in fact properties of a single substance, thereby prefiguring the modern perspective of neutral monism.
The problem of mental causation is also discussed in the context of other positions on the mind–body problem, such as property dualism and anomalous monism.
Compatibility with the conservation of energy
A more recent related objection is the argument from physics, which claims that a mental substance impacting the physical world would contradict principles of physics. In particular, if some external source of energy is responsible for the interactions, it would violate the law of conservation of energy.Lycan, William (1996) "Philosophy of Mind" in The Blackwell Companion to Philosophy, ed. Nicholas Bunnin and E. P. Tsui-James, Oxford: Blackwell Publishers. Two main responses to this have been to suggest the mind influences the distribution but not the quantity of energy in the brain and to deny that the brain is a causally closed system in which conservation of energy would apply. It could also be argued that the law of conservation of energy is false in systems which realize a mind.
Causal closure
Taking the argument a step further, it has been argued that because physics fully accounts for the causes of all physical movements, there can be no place for a non-physical mind to play a role. The principle, in slightly different iterations, has variously been called causal closure, completeness of the physical, physical closure, and physical comprehensiveness. This has been the foremost argument against interactionism in contemporary philosophy.
Some philosophers have suggested the influence of the mind on the body could be reconciled with deterministic physical laws by proposing the mind's impacts instead take place at points of quantum indeterminacy. Karl Popper and John Eccles, as well as the physicist Henry Stapp, have theorized that such indeterminacy may apply at the macroscopic scale. (See quantum mind.) However, Max Tegmark has argued that classical and quantum calculations show that quantum decoherence effects do not play a role in brain activity. David Chalmers has noted (without necessarily endorsing) a second possibility within quantum mechanics, that consciousness' causal role is to collapse the wave function, often referred as consciousness causes collapse. He acknowledges this is at odds with the interpretations of quantum mechanics held by most physicists, but notes, "There is some irony in the fact that philosophers reject interactionism on largely physical grounds (it is incompatible with physical theory), while physicists reject an interactionist interpretation of quantum mechanics on largely philosophical grounds (it is dualistic). Taken conjointly, these reasons carry little force...".
There remains a literature in philosophy and science, albeit a much-contested one, that asserts evidence for emergence in various domains, which would undermine the principle of causal closure. (See emergentism.) Another option that has been suggested is that the interaction may involve dark energy, dark matter or some other currently unknown scientific process.Robinson, H. (2003) "Dualism", in The Blackwell Guide to Philosophy of Mind, ed. S. Stich and T. Warfield, Oxford: Blackwell, pp. 85–101.
Causal overdetermination