Descartes' Rules

Descartes' Rules: An Overview

René Descartes (1596–1650), often called the "father of modern philosophy," sought to establish a foundation for certain knowledge. In his works—particularly "Rules for the Direction of the Mind" (Regulae ad Directionem Ingenii, unfinished, written around 1628) and "Discourse on the Method" (1637)—he laid out rules for how to think clearly, avoid error, and arrive at truth.

There are 21 rules in Regulae, but the most famous and influential are the four precepts from the Discourse on the Method. I'll explain both.

The Four Precepts (From the Discourse on the Method)

These are Descartes' most well-known rules. He developed them after realizing that much of what he had been taught was uncertain. He resolved to tear everything down and rebuild knowledge on a foundation of absolute certainty.

Rule Latin Phrase Explanation

1. Accept nothing as true De omnibus dubitandum (Everything must be doubted) Never accept anything as true unless you know it with absolute certainty. Avoid prejudice and hasty conclusions. Only accept ideas that present themselves so clearly and distinctly that they cannot be doubted.

2. Divide problems Divide et impera (Divide and conquer) Break every difficulty or problem into as many smaller parts as possible, as many as are needed to solve it effectively. Complex problems become manageable when reduced to their simplest components.

3. Move from simple to complex Ordo et mensura (Order and measure) Conduct your thoughts in order—starting with the simplest, easiest-to-know objects—and gradually ascend to knowledge of the most complex. Establish order even among things that do not naturally follow a sequence.

4. Review completely Enumeratio (Enumeration) Make enumerations so complete and reviews so thorough that you are certain nothing has been omitted. This ensures the integrity of your conclusions.

The Deeper Philosophical Context: Radical Doubt

To understand why Descartes created these rules, it helps to know his method of radical doubt:

Descartes realized that his senses had deceived him before. If the senses can deceive, he reasoned, perhaps everything he perceived through the senses was an illusion. He even entertained the possibility of an "evil demon" (or a powerful deceiver) systematically manipulating his perceptions.

He doubted:

· Sensory information

· Mathematical truths (could a demon make 2+2=5 seem true?)

· The existence of his own body

But he arrived at one truth he could not doubt: the fact that he was doubting. If he was doubting, he must be thinking. If he was thinking, he must exist.

This became his foundation: Cogito, ergo sum — "I think, therefore I am."

From this single indubitable truth, he sought to rebuild all knowledge using his four rules.

The 21 Rules (From Regulae)

In Rules for the Direction of the Mind, Descartes expanded his framework. Here are the most significant among the 21:

Rule Summary

Rule 1 The goal of study should be to guide the mind to form sound and true judgments about things.

Rule 2 Only focus on objects that we can attain certain and indubitable knowledge of.

Rule 3 On any subject, we should seek only what is certain—not what is merely probable.

Rule 4 Method is essential. Truth is found through intuition and deduction.

Rules 5–7 Reduce complex propositions to simpler ones; then, by intuition, ascend step by step to knowledge of the rest.

Rules 8–10 If a problem is not immediately understood, classify it and examine its simplest elements first.

Rules 11–12 Use enumeration and review to ensure nothing is missed.

Rules 13–21 Apply these principles to specific problems, reducing unknown variables to known ones and using systematic deduction.

The overall structure mirrors the four precepts but with more technical detail aimed at mathematical and scientific reasoning.

The Relationship Between Descartes' Rules and Bartlett's Law of the Lizard

This is where the connection becomes interesting. You were previously learning about Bartlett's Law of the Lizard—the idea that the primitive brain makes emotional decisions before logic ever gets a chance.

Descartes represents the opposite pole: pure rationalism.

Dimension Descartes Steven Bartlett

Core Belief Truth is found through logic, doubt, and systematic reasoning. Truth is accessed by first understanding and communicating through emotion.

View of Emotion Emotion is a source of error that must be overcome to achieve certainty. Emotion is the gatekeeper; logic cannot function until emotion is addressed.

Method Deconstruct problems, doubt everything, move from simple to complex. Activate the lizard brain (fear, curiosity, belonging) to create receptivity.

Foundation Cogito, ergo sum — thought as the foundation of existence. Emotional connection as the foundation of influence and trust.

Bartlett would likely argue: Descartes' method is excellent for analysis, but it fails as a method for communication or leadership. If you walk into a room and begin methodically doubting everything and presenting logical deductions, the lizard brains of your audience will reject you before you say your second sentence.

Descartes would likely argue: Bartlett's approach is effective for persuasion but dangerous for truth-seeking. If you bypass logic to appeal directly to emotion, you risk manipulating people—or being manipulated yourself—into believing things that are not certain.

A Synthesis: When to Use Each

A practical takeaway might be:

Context Apply

When you are thinking alone, analyzing a problem, or building a strategy Use Descartes' rules. Doubt assumptions, break problems into parts, verify your logic, review completely.

When you are leading, persuading, selling, or communicating with others Use Bartlett's Law of the Lizard. First, connect emotionally. Earn trust. Create curiosity. Then, once the lizard is calm, you can invite the neocortex to engage with the logic.

Bartlett himself acknowledges this indirectly. The structure of The Diary of a CEO begins with The Self—mastering your own psychology—before moving to The Story—communicating with others. Descartes would likely approve of the introspective rigor of Part 1, even if he found Part 2 uncomfortably emotional.

Summary Table: Descartes' Four Precepts

Rule Meaning Application

1. Doubt Accept nothing as true without certainty. Question assumptions. Verify sources. Distinguish opinion from fact.

2. Divide Break problems into smaller parts. Simplify complexity. Address one variable at a time.

3. Order Move from simple to complex. Build foundational knowledge first. Do not skip steps.

4. Review Make enumerations complete. Double-check your work. Ensure nothing is omitted.