How Descartes Methodology contributed to the First Cartesian Error

Recapping the first Cartesian error

In the previous post I explained that the first Cartesian error is the belief that ‘mind’ or ‘mental activity’ is pure cognition and that ‘body’ is an unthinking machine, responsive only to pleasure and pain and having nothing to do with cognition. I say this because Descartes begins the Passions of the Soul with the claim that the soul is the mind, the nonphysical source of thought, and the body is its vehicle; physical, extended, sensitive and mobile.

A couple of other important background points: He believes that by the 17th century there had been little progress in understanding true human nature, in explaining ourselves to ourselves (You may agree!); and he believes his problem solving method will enlighten us as to the nature of dualism.

Descartes’ method

Descartes’ method, as explained in his justly famous and immensely influential work, Discourse on the Method, has four parts:

  1. Never accept anything as true that you can’t obviously accept as true.
  2. Divide each of the problems you are examining in as many parts as you can
  3. Develop your thoughts in order, beginning with the simplest and easiest to understand
  4. When you go to review, make sure you establish every indubitable claim possible and every link you possibly can among them and check that everything you’ve included is correct.

Descartes was convinced that this method, with its fundamental premise of breaking down problems into their smallest possible components, lead him to offer a good explanation why humans’ smallest parts are the nonphysical mind and mechanical body. In his words, “I had little trouble finding which propositions I needed to begin with, for I already knew they would be the simplest and easiest to know”.

It’s of course convenient that this split fit with his bedrock beliefs. However it turned out to be very inconvenient that his method is based on confidence that no falsehoods were accepted.

Unfortunately, Descartes combination of assumptions and methods leads to what he sees as the immediate, unassailable result that the exclusive function of the soul is thought and that everything else is the function of the body – exclusive meaning only the soul can think and the soul can do nothing but think. As we’ll see, his initial assumptions taken together lead to disastrous results.

Descartes’ method absolutely depends on as much rigor as possible in establishing the ‘first principles’ to be used, but he refuses to challenge mind-body dualism because it is obvious to him, partly because he thinks the emotions are actually evidence for it. He argued that emotions are the perfect wedge with which to pry open the secrets of how dualism works, thereby explaining the essence of humanity. And the way he set things up, in this book he had to find a way to show that the emotions are evidence of dualism.

So, to summarize, Descartes method of breaking down problems into their bits leads to a need to understand the two basic parts of a person, the mind and the body. This understanding takes the form of the attribution of functions to each part, and the only function of the soul is to think.

An unforced error

Descartes could have started his project in other ways than breaking the world up into thinking souls and inanimate machines. For instance, he could have started by considering all the capabilities of humans, such as abstract thought, hunting and lifting heavy objects, and categorized them as things that can be done by: only humans, by animals, and by inanimate objects such as pneumatic or water-powered tools.

But because of his deep commitment to dualism and mechanism he decided to categorize all activities as either something we know from experience can be performed by bodies (such as our own), or as activities that couldn’t possibly be done by such inanimate machines. Since his assumptions and method led him to see the human body as nothing more than a machine with interacting parts, that when set in motion can perform various actions, but when not set in motion does nothing, he then asked himself what could a machine never do?

The ‘obvious’ answer is whatever the soul does, because what else is there? You’re probably thinking, wait, common sense tells me that, e.g. dogs and monkeys don’t have souls and they aren’t robots – they have mental lives and are capable of all sorts of complicated behaviors. But Descartes couldn’t agree; since animals don’t have souls, and since the best science of the time said animal bodies are machines (that happen to run on hot blood and muscle tension rather than water or rope tension), they are simply robots.

[[A fascinating side note: Descartes was well aware of, and fascinated by, stories of amazingly lifelike automata from Europe and China from as early as the 13th century. There is even speculation that he himself was deeply involved in creating such robots, but these stories are impossible to verify. But it seems very likely that he knew of Leonardo Da Vinci’s production of robots.]]

Of course, a science that says robots can be complicated enough to live the ‘lives’ of tigers and orangutans and pigs is capable of quite a lot. That’s probably why Descartes concluded that only the body can create and use heat to create movement and the soul, and only the soul, can think: “we do right to believe that every kind of thought within us belongs to the soul” and “it is an error to believe that the soul imparts motion and heat to the body”.

In perhaps his most famous work, Meditations on First Philosophy, Descartes gives a bit more explanation, saying that mind is “a thing that thinks…a thing that doubts, understands, affirms, denies, wills, refuses and which also imagines and senses”. (But not emotes!)


Be clear that the error I’m worried about here is not that he believes in souls, (though I do not), after all there’s many ways to think of souls. The fundamental error here was deciding that thinking has absolutely nothing to do with the body. As we’ve seen, Plato, Aristotle, and Lucretius each gave good reason to believe that thought is dependent upon and deeply engrained with human flesh. But Descartes chose to reject out of hand any evidence of that, and instead to argue for his “obvious” assumptions.

In the next post we’ll take up the second Cartesian error.


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