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Rene Descartes in five points

 


The bullet-point presentation of Cartesian philosophy. 

I have in earlier posts sought to summarize others of the Great Thinkers of the philosophical canon in five tenets per head.  Today we take on Rene Descartes.  In some respects, this may seem an idiosyncratic take on Descartes, and it is a take I would be prepared to modify in the face of appropriate contrary explanations, but it is honestly and painstakingly arrived at.  

That said: Rene D was trying to tell us .. 

1. That if we try to doubt everything that can be doubted we will end up forced to a choice between accepting the existence of a benevolent God (a postulate that can guarantee the reliability of our senses and our reason), OR accepting solipsism. 

2. Having accepted God for this purpose, we don't really have much day-to-day use for Him.  The physical world is a mechanism, just matter in motion where objects push each other around and can be exhaustively understood in those terms.

3. Matter and space are essentially the same, so physics and geometry are the same, and physics can proceed by the same a priori reasoning as geometry.  

4. Likewise, mind and thought are the same, so psychology and logic are the same, and psychology can proceed by a priori reasoning -- to the conclusion, for example, that a dreamless sleep state is impossible. 

5. Matter and mind are essentially different -- so different indeed that it is difficult to see how events in either realm can cause events in the other -- but Descartes was content to wave at the pineal gland as a possible point of intersection and to punt the difficult questions here forward to the next generation of philosophers.


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  1. HenryDecember 22, 2025 at 11:47 AM

    Christopher, I am not knowledgeable about Descartes, so I won't challenge anything you've written, but I don't understand some of it. In #3, what does "essentially" mean? Are they the same or aren't they? And, between physics and geometry, which is matter and which is space?

    In #4, I understand that "a priori reasoning" refers to logic rather than psychology, but how can a priori reasoning tell us that a dreamless sleep state is impossible? Also, suppose that scientists could establish empirically that a dreamless sleep state is impossible. Would you say that they'd used psychology to do so? I would say that they'd used biology.

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    1. ChristopherDecember 23, 2025 at 12:38 AM

      Physics generally describes matter and geometry describes space. A vacuum is, definitionally, empty space. Thus, if we find that space simply IS matter, we have reason to infer that there can be no vacuum. This in turn contributes to a picture of the world in which there is no "action at a distance" such as the operation of gravity as a force. Everything is the pushing around of matter by adjacent matter. I was using "essence" above as an implied contrast with "conventional". There may conventions that lead to regarding some questions as matters of physics and others as matters of geometry, but in essence they are the same. Cartesians did battle royale against Newtonian ideas when the time came. (Though Newton, in creating calculus, was of course drawing on the earlier generation's mathematical advance in creating analytical -- Cartesian -- geometry.)

      Likewise, Cartesians contended that the human soul cannot have a dreamless sleep, though we often fail to remember dreams. Why? Well, because "cogito ergo sum". If we cease of "think" in some manner, such as entertaining dream images, then we seek to exist. To expect that we could cease to exist and then come back into existence as if there was a continuous person underlying ... that would be to expect an odd bundling of miracles.

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    2. ChristopherDecember 23, 2025 at 12:42 AM

      Another point: if scientists could establish that a dog or a monkey has no dreamless sleep, THAT would be a use of biology. But such creatures have no souls, that is, they have no "cogito" in the sense that Descartes finds in himself and extends to other humans. The discussion of the logical implications of that "cogito" is an exercise in logic, and THEREBY in psychology if we agree in combining the two.

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  2. HenryDecember 23, 2025 at 6:36 AM

    If we think, then we exist, does not imply that if we don't think, then we don't exist. That is invalid reasoning from the inverse. If it rains, then the ground gets wet does not imply that if it doesn't rain, the ground doesn't get wet. I could pour a bucket of water on the ground.

    I trust that you are attributing to Descartes, and not stating as a fact, the view that dogs and monkeys have no souls and do not think in the sense that humans do. In reality, souls do not exist in humans or animals, and dogs and monkeys think. Whether they think in the sense that humans do depends upon how one defines "sense."

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