Cartesian Doubt and My Disagreements with Rene Descartes

Jack McDonald
3 min readNov 20, 2020


In this brief writing, I work to explain my agreements and point of disagreement with a strange yet core belief of one of the most influential philosophers of the modern era, Rene Descartes.

Before I get into that, I’ll give a brief background on who he was. Rene Descartes was a French born philosopher, mathematician, and scientist. His novel beliefs and work challenged the norms of science and math and created a new union between religion and scientific works. I’m not going to dive too heavily into Mr. Descartes background in this writing, but if you’re interested and want to learn more, I recommend that read this.

Cartesian Doubt

A foundational belief of Rene Descartes was the idea of radical skepticism. In his writings, Descartes described the methods by which to practice this belief in the following words “[doubt] everything there [is] to doubt.”

Simple enough right?

Not so much.

The reasoning behind this practice was much more complex than what might come to mind after one reading of the quote. Throughout his life, Descartes struggled to understand the true meaning of certainty, at least in its absolute form.

By doubting everything there is to doubt, Descartes believed that he was removing assumptions and ingenuine findings, and, as a result creating and realistic perspective through which to view a given situation.

Take an example:

Let's imagine I asked you to come to my birthday party that’s being held a week from now. There isn’t a scheduling conflict on your end and we’ve known each other for a few years now, so you say that you definitely make it.

Seems like a no-brainer right?

If you were exercising Cartesian doubt, you would, instead of thinking about the reasons for you to make it, work to understand the possible reasons you’d be unable to come.

For example, here’s a list of things that could impede on you plans to make it to my party:

  • Child getting sick
  • Yourself getting sick
  • Family member passing
  • Traffic accident
  • Bad weather

This list isn’t, of course, confined to just five items, just the opposite in fact. An infinite number of other inconveniences could ruin or delay your otherwise happy day.

The means by which Rene Descartes would look at a offer like the one I hypothetically offered you would not be from the perspective the likely of you arriving at the party based off of your desire to attend, but rather based off of the certainty of the above inconveniences occurring.

While it seems rather obvious that these troubles would not effect you in the next seven days, the lack of complete certainty forces you to shift your answer from “I’ll definitely be there” to “I’d love to go.”

A Brief Rebuttal

For many, this approach to opportunity doesn’t seem rational, and it really isn’t in most all circumstances. Despite this, I find it important to discuss the validity of this claim.

First off, Descartes approach actually make sense mathematically, there is no disputing that. However, what one can dispute is the means by which we break down the certainty of very things that create uncertainty.

For instance, a traffic accident could delay of cancel your plans to attend a party I’m hosting, but how is it possble to know the car accident will take place? In short, you can’t. While it’s possible to cross-reference stats about an person’s demographics with a database of those in accidents, the result is rarely telling.

These kind of calculations could create insignificant understandings of your own driving ability, but it provides no information on those around you, the state of the roadways, the organization of the roads, etc.

This is a clear hole in the argument Descartes makes. However, his principle of uncertainty allows for the possibility this type of argument to be included or excluded from the philosophy.


Hey, I’m Jack. I’m a 16-year-old developer and Innovator at The Knowledge Society. Over the past few months, I’ve been diving deep into machine learning and software development as a whole. I’m working on projects I find interesting and you might as well. Navigate to the links below to connect!






Jack McDonald

Builder exploring the impact of digital identity and credentials in the next age of the internet.