The mind-body problem was discovered by a princess

Philosophical letters from a possible Renaissance romance

Art for The Intrinsic Perspective is by Alexander Naughton

Princess Elisabeth of Bohemia—the first person to fully understand the paradoxical nature of the mind-problem, a mathematician, the possible romantic interest of Descartes, and an eventual abbess—was born in 1618, and lived in exile with her family in the Netherlands, a political refuge after her father’s brief reign. Her father’s rule had ended after he lost what was called the “Battle of the White Mountain,” for which he would be known via the sobriquet “the winter king,” having been in power for merely a season.

Elisabeth was a great philosopher in her own right—whip-smart and engaged by the intellectually stimulating times, she maintained numerous correspondences throughout her life on all manner of subjects. For her learning, within her family she was known as “the Greek,” and this was in a set of siblings that included an eventual king, another brother who was a famous scientist in addition to being a co-founder of the Hudson’s Bay Company, another sister who was a talented artist, and a further sister who was the eventual patron of Leibniz. Mathematician, philosopher, theologian, and politician, Elisabeth was, in her day, an important hub in that republic of letters that would become science.

The princess and Descartes only met in person a few times, but maintained a long correspondence over the years, exchanging a total of fifty-eight letters that have survived (more may not have). The correspondence began in 1643, and would last, on and off, until Descartes’s surprising death in 1650 (he died of pneumonia after being forced to wake early in the morning and walk through a cold castle to tutor a different and far more demanding queen). In the princess and the philosopher’s letters, Descartes usually signed off with “Your very humble and very obedient servant” and Elisabeth with “Your very affectionate friend at your service.”

Their letters are vivid historical reading—the two’s repartee is funny and humble and courteous, intimate and yet respectful of the difference in their classes (Elisabeth’s far above Descartes’s); but they also dig deep into Descartes’s philosophy, with Elisabeth always probing at holes and Descartes always on the defensive to cover them. The first letter we have is from Elisabeth to Descartes, and outlines her initial objections to his famous theory of dualism: specifically, she questions how his dualism can account for interaction between mind and body. She writes:

When I heard that you had planned to visit me a few days ago, I was elated by your kind willingness to share yourself with an ignorant and headstrong person, and saddened by the misfortune of missing such a profitable conversation. . . . But today M. Pollot has given me such assurance of your goodwill towards everyone and especially towards me that I have overcome my inhibitions and come right out with the question I put to the Professor, namely: Given that the soul of a human being is only a thinking substance, how can it affect the bodily spirits, in order to bring about voluntary actions? . . .

In writing to you like this I am freely exposing to you the weaknesses of my soul’s speculations; but I know that you are the best physician for my soul, and I hope that you will observe the Hippocratic oath and supply me with remedies without making them public.

Descartes responds with a long letter in turn. First, he says that last time they spoke in person he had been so struck by her beauty he was unable to say anything intelligent, and is much more comfortable corresponding via writing like this. With regards to her question of how the soul (or mind, in our current parlance) could interact with the body, Descartes admits:

I can’t hide anything from eyesight as sharp as yours! . . . In view of my published writings, the question that can most rightly be asked is the very one that you put to me. All the knowledge we can have of the human soul depend on two facts about it: (1) the fact that it thinks, and (2) the fact that being united to the body it can act and be acted on along with it. I have said almost nothing about (2), focusing entirely on making (1) better understood. . . .

Trying to understand weight, heat and the rest, we have applied to them sometimes notions that we have for knowing body and sometimes ones that we have for knowing the soul, depending on whether we were attributing to them something material or something immaterial. Take for example what happens when we suppose that weight is a “real quality” about which we know nothing except that it has the power to move the body that has it toward the centre of the Earth. How do we think that the weight of a rock moves the rock downwards? We don’t think that this happens through a real contact of one surface against another as though the weight was a hand pushing the rock downwards! But we have no difficulty in conceiving how it moves the body, nor how the weight and the rock are connected, because we find from our own inner experience that we already have a notion that provides just such a connection. But I believe we are misusing this notion when we apply it to weight—which, as I hope to show in my Physics, is not a thing distinct from the body that has it. For I believe that this notion was given to us for conceiving how the soul moves the body. . . .

Your letter is infinitely precious to me, and I’ll treat it in the way misers do their treasures: the more they value them the more they hide them, grudging the sight of them to rest of the world and placing their supreme happiness in looking at them.

Descartes is talking, we should note, about gravity, not merely “weight.” His reasoning seems to be that the mind is like a force, similar to gravity’s force, because gravity operates “at a distance” (or at least, appears to)—it is not like a billiard ball hitting another one. But his reasoning here is quite sparse, and we can already notice it is rather weak, since gravity is of course a physical phenomenon. Elisabeth senses this too, and does not let the point go. She writes:

The old idea about weight may be a fiction produced by ignorance of what really moves rocks toward the centre of the earth (it can’t claim the special guaranteed truthfulness that the idea of God has!). And if we are going to try theorising about the cause of weight, the argument might go like this: No material cause of weight presents itself to the senses, so this power must be due to the contrary of what is material, i.e. to an immaterial cause. But I’ve never been able to conceive of “what is immaterial” in any way except as the bare negative “what is not material,” and that can’t enter into causal relations with matter!

Elisabeth is saying: if the mind is a physical force that’s undiscovered, Descartes’s reply would make sense, but his dualistic theory is such that, very explicitly, the mind is definitionally nonphysical (immaterial) and so therefore it is totally unimaginable how it might interact with the physical (material). In another letter, Elisabeth goes on to say:

I find from your letter that the senses show me that the soul moves the body, but as for how it does so, the senses tell me nothing about that, any more than the intellect and the imagination do.

Although, as always, she ends with a note of respect:

I owe you this confession . . . but I would think it very imprudent if I didn’t already know—from my own experience and from your reputation—that your kindness and generosity are equal to the rest of your merits. You couldn’t have matched up to your reputation in a more obliging way than through the clarifications and advice you have given to me, which I prize among the greatest treasures I could have.

Despite the princess’s diplomatic end, it is clear Descartes had been ducking the question. And he really did duck it: no reply to this letter is known, although it is possible there were other, secret letters. The princess wished their letters kept private, and it was only long after her death that the full correspondence was published, and it seems unlikely it all survived. We certainly know that their correspondence continued on concerning other matters, like geometry problems and their personal lives—including an original proof, on her part, of a mathematical problem: given that there are three circles on a particular plane, find a fourth circle that touches all of them. Descartes told her of the problem in a letter and the princess worked on it at the same time he did. They both arrived at the same conclusion, but Descartes conceded that her proof was more elegant (and this is objectively true, as Elisabeth’s proof contains fewer terms). Descartes even dedicated his book Principles of Philosophy to her, acknowledging in the dedication her perspicacity:

The biggest reward I have received from my published writings is that you have been so good as to read them, for that has led to my being admitted into the circle of your acquaintance, which has given me such a knowledge of your talents that I think that it would be a service to mankind to record them as an example to posterity.

Perhaps it is only the bosom nature of the age, but I cannot help but read these letters of philosophy as love letters. Two nerds, stuck in the Renaissance, exchanging the emails of the day, meeting only a few times in person, perhaps under the auspices of great passion. And scholars have indeed speculated about a romantic liaison. For there are some (utterly inconclusive, merely suggestive) reasons to think this may be more than historical fan fiction: When Descartes died, Princess Elisabeth was said to have been devastated. And she advocated tirelessly for both him and his philosophy during her life, even after his death. Living until seventy-two, she never married, indeed even turned down a marriage proposal from a prince (at least partly for religious reasons), yet she lived a rich life as a spinster, promoting the new philosophical and scientific ideas to elite society, advocating for various intellectuals to get professorial positions at universities, and corresponding with great thinkers. She ultimately joined the church to become an abbess in the Rhine Valley and governed wisely over more than seven thousand people until 1680. Leibniz reportedly sat at her deathbed.

Elisabeth lived a grand life of political intrigue, duty, and intellectual connectivity, but her philosophical critique of interactionism means that the princess was perhaps the first person in history to state the paradoxical nature of the mind-body problem clearly and explicitly. Consciousness seems irreducible to the material, and yet we also know, as Elisabeth was the first to point out, that the two cannot be completely separate, for then they can never interact. We have run very far since 1643, but in another sense we have ended up back at the same place.

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