How Can Souls Move Bodies? Descartes and Princess Elisabeth of Bohemia

Introduction and Context:
In the previous post we got a quick introduction to substance dualism (aka Cartesian dualism), the idea that the mind/soul and the body are not one and the same and are therefore fundamentally distinct substances.  That is, your brain is not your mind and your mind is not your brain.  We looked at two of the arguments that Descartes gave for the position and some of the objections.  Whether we find the arguments convincing or not, most psychological studies show that most people are dualists (but few philosophers and neurologists are).  There are also some contemporary arguments for different types of dualism which we'll look at in later posts but for now we're going to focus on substance dualism.

Setting all that aside, supposing we are convinced that dualism is true, it's interesting to consider what difficulties this position might give rise to.  Descartes' contemporary, Princess Elizabeth of Bohemia (who's momma didn't raise no fool) brought up some of these problems to Descartes himself in their written correspondence.

The Interaction Problem
At the heart of the problem with dualism is the interaction problem:  how is it that something that doesn't have any physical properties (i.e., doesn't exist in space, has no extension, and has no mass) can interact causally with something that is physically extended and has mass? and vice versa...  

So, how is it that thoughts in the mind (which have absolutely no physical properties) can causally bring about actions in a physical body?  Or that something happening to the body (e.g., stimulation of our perceptual organs or being poked by a needle) can bring about perceptual experiences and thoughts (e.g., "I see a red chair" or "ouch! that freakin' hurt!")  It would seem that for anything to causally affect a physical body it too must be physical or at least have some minimal physical properties like mass and extension (unless you want to invoke magic).

To see how Descartes responds to the interaction problem, Let's take a look at the back and forth in the letters between the two and see if he gives a satisfactory response.

May 21, 1643:  Descartes' First Attempt
The reason it seems like there's an interaction problem between mind and body is because I haven't explained how they interact yet!  The goal of the Meditations was only to give the notions of body and soul that explained why they are 2 distinct substances--not to explain how they interact. But now that you're asking...

Also, although I only discussed the notions of body and mind that allow us to distinguish them, it doesn't mean that there aren't additional notions we can appeal to that explain how the two interact.

The confusion arises because you are using the notions that allow us to distinguish between the two to try to explain how the two interact.  But this obviously won't work because we're missing the relevant explanatory notions!

He then gives Elizabeth an analogy to illustrate his point:
The scholastics (the tradition of philosophy that Descartes opposed) believed that there was a "thing" called "heaviness" that caused objects to fall to the ground.  But they were misunderstanding the notion of heaviness.  Yes, having "heaviness" is why objects fall to the earth, but the scholastics misunderstand "heaviness" as being an actual thing that physically causes the object to fall.  They were misapplying concepts, this is why they were confused.

Something along the same lines is happening when we talk about the properties we attribute to our bodies and minds to account for how they interact.  We are mis-conceptualizing and misusing the properties, and this is the cause of our confusion.

To summarize, (1) He sort of explains why, given the incomplete descriptions of mind and body that he's given, we can't understand how mind and body interact. However, (2) he avoids ever giving an answer to the interaction problem.

June 10, 1643:  Elizabeth's Reply
Before I begin, I just want to point out that Elisabeth's writing is a stunning example of the principle of charity. Descartes' initial reply was unconvincing at best and totally side-steps the problem at worst. But look how Elizabeth replies

Now the interests of my house, which I must not neglect, now some conversations and social obligations which I cannot avoid, beat down so heavily on this weak mind with annoyance or boredom, that it is rendered useless for anything else at all for a long time afterward:  this will serve, I hope, as an excuse for my stupidity in being unable to comprehend [the "heaviness" example that Descartes gives to explain why the interaction problem isn't really a problem, but simply the result of not having or misunderstanding the notions for explaining how interaction occurs].

Ah! If only facebook and youtube disputes had this much civility....(meh...they wouldn't nearly be as much fun).

Ok, on to her reply...
In short she says, even with the "heaviness" example, I still don't understand how an immaterial thing that doesn't exist in space or have mass or extension can causally interact (via contact) with a physical thing (i.e., the body).   I cannot conceive of an immaterial thing as anything but the negation of matter, and in order for matter to move, it must be acted upon by physical force and contact (none of which are possible for an immaterial substance to do).

In fact, it would be easier for me to think of the soul as being material than to conceive of how something non-material could causally interact with something material.

(Bonus information: Locke, writing just after Descartes, actually suggests this as a solution: If God can do anything, why could he not create matter that can think?)

Information?
Always the helpful one, Elisabeth offers Descartes a possible solution:  One possibility would be that the soul moves the body by communicating information to it, however, the information can only be interpreted and understood by the body if the body possesses intelligence...and Descartes denies that matter can be intelligent..Doh! So, that's not going to work...

June 28, 1643: Descartes Second Reply
In short, Descartes still doesn't offer a direct answer.  He says that since it is easier for her Highness "to attribute matter and extension to the soul than to attribute to it the capacity to move a body and to be moved by one without having matter" she should feel free to attribute the matter and extension to the soul.  By doing so she will be able to conceive of the union of soul and body, even though in reality they are two distinct things.

This reply is quite unsatisfactory because (a) if the soul is not extended (as Descartes maintains) how will conceiving it as such explain away the interaction problem?  Also, (b) if we are to conceive of the union of body and soul as Descartes instructs us, presumably this would involve conceiving of some sort of causal connection, but that's precisely the thing that Elizabeth is not able to conceive of!

Clearly irritated by the fact that he can't come up with a good answer, Descartes ends his letter by admonishing Elizabeth for being too philosophical!

Finally, though I believe it is very necessary to have understood well once in one's life the principles of metaphysics, since it is these that give us knowledge of God and of our soul, I also believe that it would be very harmful to occupy one's understanding often in meditating on them [...]

Lol.

Now, we're getting into facebook-fight territory!  At this point I think Descartes would have blocked her...

Sept. 13, 1645:  Elisabeth's Reply
Up until now, Elisabeth was primarily focused on asking how the immaterial mind could causally influence the actions of the material body.  Now, she asks for clarification on the other side of the interaction problem:  How is it that the "passions" (i.e., bodily feelings like hunger or physical pleasure) can interact with the non-material mind to influence our thoughts?

The Passions of the Soul  (Not of particular philosophical import)
Descartes wrote The Passions of the Soul largely as a response to Elisabeth's request for more information on the interaction between the passions and the immaterial mind.

First he lays the groundwork for how to distinguish between things that pertain to the soul and things that pertain to the body: 
(1) Anything that we can experience as being in us and which we see as existing in wholly inanimate bodies must be attributed to our body; 
(2)  Anything that we cannot conceive of as belonging to a body must belong to the soul.

From (2) it follows that thoughts belong to the soul.  From (1) it follows that heat and movement belong to the body.

17C Physiology and Anatomy 101:  How the animal spirits (the stuff that causes bodies to move) cause movement:
The animal spirits (tiny particles that 17C physicians believe to be responsible for animation) are contained in the blood.  They are very very fine particles.  The heart pumps them up to the brain where they enter cavities and go through pores thereby coming in contact with the nerves and then the muscles.  That's how bodies moves...(!)

How does the body move without the soul?
Sometimes the animal spirits can cause some pores to open or close more than others, which in turn causes a muscle to contract more or less.  The sensory nerves can cause the pores to be opened more or less than usual, which in turn causes the animal spirits to change direction and go to the muscles in such a way that causes the body part to move as it usually does for such an occasion.

In short, our bodies are self-sufficient robots. Our sensors cause the animal spirits to open and close pores which in turn direct the animal spirits to the correct muscles for the appropriate movements.

The function of the soul:  In this mechanistic framework you may be asking where our soul/mind is in all this.  The soul is the "place" where we have our thoughts of which there are 2 main kinds:  actions of the soul and passions of the soul.  Actions of the soul are our volitions since we experience them as coming from our soul. The passions of our soul are the various perceptions we have since they are externally caused.

How do the soul and body interact?  Through the pineal gland in the brain.

How do we know the pineal gland is the "seat of the soul"?  All of the organs for our external senses come in twos (eyes, hands, ears, and so on...)  (Ignore that you only have one tongue and one mouth, 10 fingers, etc..!)  There must be a place where the two images coming in the two eyes or the double organs of any other sense converge to form a single image or impression before reaching the soul--otherwise the soul would see two of the image!  That's science!  ...well, 17C science anyway...

(Sadly, there are people who still believe this!!!)