The “mind/body” problem has been a major source of philosophical debate since pretty much the beginning of philosophical debate. Philosophers call the belief that the mind and body are separate “dualism” and the belief they aren’t “monism.” Dualism typically leads to all sorts of appealing stuff including an immortal soul or even the entire universe being conscious–just like us! Monism tends to foster more depressing beliefs like all our conscious experience, that whole what it’s like to be something thing, is the result of brain activity and when that stops, the party’s over—or as Christopher Hitchens put it “the party will still go on, you just have to leave[1].” Many thick philosophical tomes have been written about this, but I’ll try to sum up the debate with two heralded representatives. On the dualist side, René Descartes and for the monists, Baruch Spinoza.

René Descartes argued that mind (or soul) and body are fundamentally different substances. The mind is a non-physical, thinking substance, while the body is a physical, extended substance. He famously said “Cogito, ergo sum” (I think, therefore I am) meaning everything can be doubted to exist except the fact he is thinking. From this, he concludes the thinking thing (mind) must be distinct from the body because the certainty of his existence is rooted in the act of thinking, not in having a body. He further argued that physical bodies can be divided into parts, but the mind cannot. He argued that the mind is a unified, indivisible entity, while bodies are extended and divisible so mind and body must be of different natures. This created a problem for Descartes in that mind and body clearly interact with each other. If one’s finger is physically poked with a pin, it causes a mental experience, pain. He solved this problem by identifying a particular part of the brain, the pineal gland, as the primary site of interaction between the mind and body. Sadly, this theory has not held up to reason. We’ve learned that the pineal gland is a little melatonin factory, that drives things like our sleep cycles, rather than the transfer station between body and soul.

Spinoza’s defining thought and extension as the two attributes we’re able to perceive has led some to mistakenly believe he was also a dualist. In fact, he was a staunch monist, believing that all of reality is composed of a single substance (God/Nature). Spinoza specifically rejected Cartesian dualism in favor of parallelism, the idea that the mind and body are not separate substances but rather two expressions of the same substance. That they are different things does not mean they’re completely distinct any more than a shadow can be considered as being totally separate from the body that causes it. For every event in the body, there is a corresponding event in the mind, but neither “causes” the other. They run in parallel because they are two aspects of the same reality.

Spinoza specifically rejected supernatural notions, a soul that transcends the body for example, that dualism typically generates. To Spinoza everything that exists is within Nature, not outside it. From this perspective, the human mind (thought) and the human body (extension) are just two “views” of the same reality. The same thing that is happening “physically” in your body is also happening “mentally” in your mind, but neither one causes the other because they are just different perspectives on the same event.

Who was right? What has reason revealed that might help us answer this question?

Philosopher and journalist Julian Baggini’s 2011 book “The Ego Trick” makes a compelling argument, backed up by the latest neuroscience, that dualism is a “category error.” The error is in mistaking two aspects or perspectives of something as being two distinct things–as in the above shadow example. The emerging neuroscientific consensus is that consciousness results from a particular pattern of activity in the brain. Baggini notes that this activity does not come from a particular part of the brain but rather from many different areas of the brain simultaneously. He cites as evidence how people who suffer damage to particular parts of their brain experience changes in specific personality traits, while other traits remain the same. Baggini argues that mistaking consciousness as being separate from brain activity will force you to have to solve Descartes’ interactivity problem. If, however, you accept that consciousness is a function of brain activity, there is no interactivity problem to solve.

Imagine arguing that a computer’s software and hardware are totally separate things and then trying to explain how software can “control” hardware. The reality is that “software” is just a description of a pattern of organization that exists within the hardware. You can’t separate them — the “software” doesn’t exist independently of the hardware. Software cannot exist without hardware and hardware without any software is a dead body. We often say “my mind” as if it’s a separate possession from “my body,” but this is a linguistic illusion.

Spinoza’s monism and his refusal to accept Descartes’ “two substances” has had a lasting impact on philosophy, neuroscience, and even cognitive science. Baggini’s argument that dualism is a category error is a modernized, evidence-backed, and I would argue clearer, version of the one Spinoza made.

Here’s a simple table comparing Cartesian dualism, Spinozian monism and modern philosophy and neuroscience represented by Julian Baggini’s “category error.”

Cartesian Dualism	Spinoza’s Monism	Baggini’s Category Error
Mind and body are separate substances	Thought and extension are attributes of the same substance	Mind and body are distinct categories, but not distinct substances
Mind and body interact	Mind and body are in parallel (no interaction needed)	No “interaction” is required because they are aspects of the same whole
Two independent realities	One substance, perceived as two modes (thought/extension)	Confusion comes from misapplying conceptual distinctions to reality
Language reflects reality	Language creates false distinctions	Thinking that mental and physical are separate is a conceptual mistake
Interaction is mysterious	No interaction needed (like two sides of a coin)	No causal link required, only conceptual clarity

If you start from Descartes’ assumptions, the mind-body problem seems unsolvable. But if you follow Spinoza (and modern neuroscience), you realize it was never a real problem to begin with. The real challenge isn’t solving it—it’s accepting the answer. As a bonus, you get to avoid spooky or supernatural explanations of how a “soul” interacts with a “body” and bask in the glow of the power of reason!

This perspective doesn’t just solve the mind-body problem — it dissolves it.

Dualism as a philosophical idea is nearly dead and in an irretrievable coma as a scientific proposition. While my argument has been focused on Cartesian dualism, the many modern versions, including property dualism, panpsychism (aka neo-dualism), epiphenomenalism (a weird cousin of dualism) and supernatural dualism are all essentially “god of the gaps” arguments. They sidestep all we’ve learned that refutes dualism, point to something we’ve yet to figure out (Qualia!) and then declare that consciousness is a “hard problem” we will never solve. Philosophers like David Chalmers, a serious and seriously smart dude, speculate that consciousness may always remain an unsolved mystery, and he could be right. But history shows that when we label something “unexplainable,” it often just means we haven’t explained it yet. As our knowledge of consciousness increases, we will hopefully begin to chip away at the “hard problem.” The likelihood that any of the current speculations about the origin or purpose of consciousness will turn out to be the final word seems vanishingly small, especially if they are supernatural in nature. Reason shoots down supernatural and metaphysical explanations far more often than it confirms them. Why should consciousness be any different?

Despite all we’ve learned, dualism continues to thrive in the minds of most humans. We find it hard to accept that our super-awesome thoughts are actually just fleeting neural impulses. It’s way more fun to assign cosmic status to our thoughts, not because of any evidence, but because it flatters our egos and, perhaps most importantly, lets us believe the death of our bodies is not the end for us.

To paraphrase Jay-Z “We got 99 problems but mind/body ain’t one.”

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[1] Hitchens was talking about mortality when he said this but I think it still fits