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One of the longest-running debates on the nature of humanity is regarding the nature of “the mind” and whether or not it is separate from the brain. Descartes and Spinoza were philosophical rivals, the twin pillars on which modern philosophy is founded, and whereas the former pioneered “Cartesian Dualism,” arguing for the separate coexistence of the physical and metaphysical self, “Spinozan Materialism” holds that everything is composed of a single substance (i.e., atoms) forming a singular, Monist “whole.”

Thinkers as diverse as Plato, Rumi, Aquinas, and Dostoevsky believed in something akin to a “soul” separate from the brain, while the likes of Hume, Voltaire, Nietzsche, and Sartre scoffed off this idea.

Christian neuroscientists such as Michael Egnor are now reviving this age-old debate. How are they doing so, and why?

Neo-Dualism and Neuroscience

Egnor references Descartes, likening his dualism to a belief in “the ghost in the machine.”

Descartes’ famous saying, “I think, therefore I am” is a triumph of a priori reasoning. From that non-evidential, non-material reasoning along with geometrical axioms (e.g., a triangle always has three sides, and your senses cannot “make” you think otherwise) for his existence, he believed he could axiomatically prove the existence of God and the soul. Neuroscientists such as Egnor point to cases such as split-brain patients as a new proof of a “self” independent of the material brain. Patients’ brains may be split and their cognitive functions impaired, Egnor argues, but their “will” remains unified.

Materialism and Free Will

So why does this matter?

Because it’s hard to ascribe morality to someone who doesn’t have control over their actions. For Egnor and dualist philosophers before him, this forms the moral impetus behind dualism. If everything is governed by causality, there is no free will, in which case, they posit, morality cannot exist, and without morality, life is bleak beyond possibility.

There are, of course, rebuttals to that. Thinkers as radically different as the Catholic Aquinas and the atheist Hume embraced Compatibilism, which admits to the laws of causality restricting free will while still making a case for its existence.

Neuroscience may reframe the body/soul question as a brain/mind one, but the material substance of the debate seems set to continue forever. That much, at least, seems simply out of our control.