Discourse on the Method of Rightly Conducting One’s Reason and Seeking Truth in the Sciences

René Descartes

CONTEMPORARY TRANSLATION

Note: Descartes’ full title emphasizes not only the search for truth in science but also the correct use of one’s reason in all matters of life. This work is divided into six parts, each addressing different aspects of knowledge, method, and personal philosophy.

Introduction

This document is called Discourse on the Method of Rightly Conducting One’s Reason and Seeking Truth in the Sciences, but it’s often mistakenly shortened to Discourse on Method, which leaves out its full meaning. The book is divided into six parts:

1. Various Thoughts on the Sciences.
2. The Main Rules of the Method I Have Sought.
3. Some Moral Rules Derived from This Method.
4. Arguments Proving the Existence of God and the Soul.
5. A Discussion on Physics, Including the Movement of the Heart and Comparisons Between Human and Animal Souls.
6. What Is Needed to Further Advance Knowledge and My Reasons for Writing This.

Context: This structure not only outlines Descartes’ systematic approach to building knowledge but also hints at the personal journey behind his method—from skepticism to certainty.

Part 1: The Nature of Good Sense and My Early Studies

Good Sense Is Universal, But We Use It Differently

The ability to think and judge well—what we call good sense or reason—is something all people naturally possess in equal amounts. However, our different opinions come from the different ways we use our reason and what we choose to focus on. Simply having a good mind isn’t enough; what truly matters is how well we use it.

Even the most intelligent people can make serious mistakes, and those who think carefully but slowly can make more progress than those who rush into conclusions.

Context: Here, Descartes reminds us that intellectual capability is common, but disciplined reasoning distinguishes sound judgment from error.

My Approach to Knowledge

From a young age, I was fortunate to discover certain ways of thinking that led me to develop a method. This method has allowed me to increase my knowledge step by step, within the limits of my mind and lifespan.

At the same time, I have always been cautious in my judgments about myself and skeptical about the usefulness of many human pursuits. Yet, despite my doubts, I have gained enough confidence in my method to believe that if there is a truly valuable human endeavor, it is the one I have chosen.

Of course, I could be wrong—perhaps what I see as valuable is nothing more than illusion. But I know how easily we deceive ourselves, so I want to share my approach openly. This way, others can judge for themselves, and I can learn from their feedback.

Annotation: Descartes’ willingness to expose his method for communal scrutiny reflects his commitment to intellectual honesty and progress.

Why I Moved Away from Formal Education

I don’t intend to teach a method that everyone should follow, but simply to share how I have directed my own thinking. Some philosophers set out rules for others, assuming they are wiser, but if they make even the smallest mistake, they are to blame. My goal is different: I am simply telling my story.

Since childhood, I was encouraged to study, and I believed that books could teach me everything I needed to know. But after completing my formal education, I found myself full of doubts, realizing that my studies had only made me more aware of my ignorance.

This was not because I had attended a poor school, or because I had been lazy, or because I lacked intelligence. On the contrary, I had studied at one of the best institutions in Europe, absorbed every book I could find, and was regarded as an excellent student. Even so, I did not find the certainty I was seeking.

Context: This section reflects the shift from traditional academic learning to a more experiential, self-directed quest for truth—a turning point that influenced modern scientific inquiry.

The Value of Studying Different Subjects

I still respected my education. I recognized the importance of:

• Languages: They allow us to understand the thoughts of past generations.
• Fables and History: They help shape our judgment.
• Oratory and Poetry: They cultivate beauty and persuasion.
• Mathematics: It provides certainty and practical applications.
• Ethics and Theology: They offer guidance for life.

Yet, despite their value, I realized that none of these disciplines provided a solid foundation for certainty. For example, ancient philosophy, despite centuries of study, remained full of disagreements. How could I expect to do better than those who had come before me?

Science, too, seemed built on shaky ground. I saw little value in pursuing knowledge just for personal gain or prestige. I did not wish to deceive myself with the illusion of wisdom, as so many scholars did.

Annotation: Descartes critiques established academic disciplines for their lack of absolute certainty, setting the stage for a new approach to knowledge.

A New Path: Learning from the World Itself

Because of this, as soon as I was free from formal education, I abandoned my studies. Instead, I decided to learn from the real world. I traveled, visited courts and military camps, met people of different backgrounds, and observed human nature firsthand.

I found that practical experience often reveals more truth than academic study. In the real world, if someone makes a bad judgment, they suffer the consequences. But scholars, whose work has no real-world impact, can argue endlessly without ever discovering the truth.

Through these experiences, I developed a strong desire to distinguish truth from falsehood, not just in academic matters but in practical life as well.

Context: Descartes’ decision to rely on personal experience over traditional education paved the way for empirical methods that later defined the scientific revolution.

Part 2: The Need for a New Method

A Fresh Start in Thinking

At the time, I was in Germany, traveling with the army. One winter, while waiting for better weather, I found myself alone in a warm room with plenty of time to think. That solitude gave me the opportunity to reflect deeply on the way we acquire knowledge.

I realized that things made by multiple people—like buildings constructed by different architects—are often less perfect than those made by a single person with a clear plan. This is why cities that developed gradually over time tend to have messy, irregular layouts, while planned cities are better organized.

Annotation: Descartes uses this analogy to illustrate the importance of a unified, deliberate method in thought—a theme central to his later arguments.

Why We Must Question Our Beliefs

Human knowledge, on the other hand, has been built up over centuries by different thinkers, each adding their own ideas. Because of this, I suspected that much of what we accept as truth is based on weak foundations.

As children, we naturally accept the customs, beliefs, and values of our culture. But if we want to be sure that our beliefs are true, we must examine them carefully rather than just following tradition.

Of course, it would be absurd to try to rebuild society or science from scratch. Just as we don’t tear down an entire city just because its streets are disorganized, we shouldn’t destroy established knowledge without a plan. But I realized that, for my own thinking, the best approach was to erase all my previous assumptions and rebuild my beliefs on a solid foundation.

Context: This call for radical doubt is one of Descartes’ most influential contributions to philosophy—it encourages skepticism as a tool for achieving certainty.

The Need for a New Method

To avoid confusion, I decided to follow a structured method, much like architects and engineers do when designing buildings. I didn’t want to rely on old ideas without first testing them for reliability.

I saw that logic, as it was traditionally taught, was more useful for explaining ideas than for discovering new ones. Mathematics, on the other hand, was full of certainty, but was often focused on abstract problems without practical application. I wanted a method that combined the clarity of mathematics with the ability to solve real-world problems.

The Four Rules of My Method

After much thought, I created four simple rules to guide my thinking:

1. Accept nothing as true unless it is completely clear and certain. (I would avoid assumptions, guesswork, and anything I wasn’t absolutely sure about.)
2. Break problems down into smaller parts. (Instead of tackling big questions all at once, I would analyze them piece by piece.)
3. Think in an orderly way, moving from the simplest concepts to the most complex. (This way, I wouldn’t get lost in confusion but could build up knowledge step by step.)
4. Review everything thoroughly to ensure nothing is overlooked. (I would carefully check my reasoning at every stage.)

Annotation: These rules, inspired by mathematical reasoning, are a cornerstone of modern scientific method—emphasizing clarity, structure, and systematic doubt.

Applying the Method

To practice my method, I started with problems in geometry and algebra. I focused only on the simplest and most general principles, solving each problem in a logical sequence.

As I did this, I found that my thinking became sharper, and I was able to solve problems that had once seemed impossible. More importantly, I became confident that I could use the same method to solve questions in other areas of knowledge, including science and philosophy.

But I knew I couldn’t rush into philosophy too quickly. First, I needed to clear my mind of old assumptions and carefully prepare myself. So, I committed to spending several years gathering experiences, learning about the world, and refining my method before applying it to deeper questions.

Context: Descartes’ disciplined approach is reflected in today’s emphasis on incremental progress and peer review in scientific research.

Part 3: A Temporary Moral Code

The Need for Temporary Guidelines

When rebuilding a house, you need a place to live while construction is ongoing. Similarly, while I was in the process of questioning all my beliefs, I needed a temporary moral code to guide my actions.

Since I was still uncertain about what was ultimately true, I decided to adopt a set of practical principles that would help me live well while I worked on discovering fundamental truths. These moral rules weren’t meant to be final but were simply a way to avoid indecision in my daily life.

The Three Main Rules

I established three key maxims for myself:

1. Follow the customs and laws of my country. I decided to obey the laws and traditions of my society and to remain faithful to the religion I was raised in. In all other matters, I resolved to follow moderate and reasonable opinions, especially those held by wise and practical people. Note: This approach emphasizes stability and social cohesion during a period of intense personal doubt.
2. Be firm and decisive in action. Just as a traveler lost in a forest should pick a direction and stick to it rather than wander aimlessly, I resolved to act decisively, even when I wasn’t completely certain I was right. In daily life, we often don’t have time to figure out the absolute truth before making decisions. So, I decided that once I had chosen a course of action, I would stick to it firmly instead of constantly second-guessing myself.
3. Focus on controlling myself rather than controlling the world. Instead of wishing that the world would change to suit me, I would train myself to accept reality as it is. I would aim to master my own desires and emotions, rather than expecting external circumstances to go my way. Annotation: This rule, echoing ancient philosophical teachings, underlines the value of inner peace and self-mastery in achieving true contentment.

My True Goal: Pursuing Knowledge

Along with these moral guidelines, I decided that the best path for my life was to dedicate myself to the search for truth.

I had discovered a method that gave me intellectual satisfaction, and I felt that there was nothing better I could do than continue applying it to discover new knowledge.

I believed that if I could perfect my reasoning, I would also improve my ability to act rightly. Since our will follows what our mind believes to be true, the best way to live wisely is to think clearly and accurately.

Nine Years of Travel and Reflection

Having settled on this temporary moral code, I spent the next nine years traveling, observing people, and refining my ideas.

• I didn’t engage in academic debates but questioned everything privately, gradually getting rid of false beliefs.
• I wasn’t a skeptic who doubted just for the sake of doubting. Instead, I was like a scientist clearing away the debris before building a new structure.
• Along the way, I gathered experiences and observations that helped me form better judgments.

During this time, I continued practicing my method by applying it to mathematical problems and other fields of study. This helped me sharpen my thinking while avoiding the distractions of philosophy debates that led nowhere.

The Turning Point

At the end of these nine years, I had avoided committing to any particular philosophy, but I had gained confidence in my ability to find truth. However, people began assuming that I had already developed a full philosophical system, which forced me to take my project more seriously.

To continue my work in peace, I decided to retreat into solitude. I moved to a place where I could work quietly, away from distractions, so I could begin laying down a solid foundation for my philosophy.

Context: This period of travel and self-reflection is crucial—it marks the transition from exploratory doubt to a more focused, systematic approach that underpins Descartes’ later work.

Part 4: The Foundations of Knowledge

Doubting Everything to Find Certainty

Once I was settled in solitude, I began thinking deeply about the foundations of knowledge. I wanted to find a single, unquestionable truth upon which I could build all my reasoning.

I had already realized that in practical life, we sometimes have to follow uncertain opinions as if they were true. But in philosophy, I wanted to do the opposite: reject anything that could possibly be false until I found something absolutely certain.

I decided to doubt everything:

• I would not trust my senses, because they sometimes deceive me.
• I would not trust logical reasoning, because even in mathematics, people sometimes make mistakes.
• I would not trust the outside world, because I might be dreaming, and dreams often seem real while we are in them.

The First Certainty: "I Think, Therefore I Am"

As I was doubting everything, I realized that there was one thing I could not doubt:

If I am doubting, then I must exist as a thinking being.

Even if everything else I believed was false, the very fact that I was thinking meant that I existed.

This led me to my first fundamental principle:

"I think, therefore I am" (Cogito, ergo sum).

This was a truth so certain that nothing could make me doubt it. It was the perfect foundation for my philosophy.

What Am I? A Thinking Being

Once I established that I exist, I had to figure out what I am.

I knew I had a mind, because I was thinking. But could I be sure that I had a body?

I could imagine that I had no body, no physical senses, and no external world. But I could not imagine that I did not exist as a thinking being. Therefore, I concluded that:

• My true nature is that of a thinking being (or mind).
• My existence does not depend on my body. Even if my body did not exist, I would still exist.

Annotation: This radical dualism—that the mind and body are separate—is one of Descartes’ most influential ideas and has spurred centuries of debate on the nature of consciousness.

A Rule for Finding Truth

I then asked myself: What makes "I think, therefore I am" so certain?

I realized that it was because I clearly and vividly understood it to be true.

So, I formed a general rule:

Anything I perceive clearly and vividly must be true.

However, the challenge was knowing which perceptions were truly clear and which were just illusions.

The Proof of God's Existence

Next, I asked myself: Where do my thoughts come from?

I could imagine many things—like the sky, the stars, and physical objects—but none of those ideas seemed to require anything greater than my own mind to explain them.

But then I realized that I had an idea of a perfect being—God.

This idea of perfection could not have come from me, because I was full of doubts and imperfections. Something more perfect than me must have put this idea in my mind. Therefore, God must exist.

Context: By asserting the existence of a perfect being, Descartes argues that such a being would not allow him to be systematically deceived, thus bolstering trust in his clear and vivid perceptions.

Why This Matters

I now had two fundamental truths:

• I exist as a thinking being.
• God exists as a perfect being.

This was important because if God is perfect, he would not deceive me. Therefore, as long as I use my reason properly and only accept things that I clearly and vividly understand, I can trust my conclusions.

A Final Thought on Dreams and Reality

Some people might still wonder: How do I know I'm not dreaming?

I admitted that while dreaming, things can seem as real as when I'm awake. But dreams never contain the same kind of clear and structured reasoning that I can have when I am awake. Also, if God is perfect, then my clear and vivid perceptions must be trustworthy.

Thus, by proving the existence of myself and God, I had laid the foundation for all knowledge.

Annotation: This section not only establishes the certainty of one’s own existence but also introduces a theistic safeguard to secure reliable knowledge—a pivotal moment in modern philosophy.

Part 5: Applying the Method to Science and Medicine

Discovering the Laws of Nature

Once I had established that clear and vivid thinking leads to truth, I began applying this principle to the natural world.

I realized that nature follows fixed laws that God has established. By carefully studying these laws, we can understand how everything in the universe works.

A Thought Experiment: The Creation of a New World

To explore these laws, I imagined what would happen if:

• God created a new world out of pure matter.
• He set this matter into motion without any special design—just random movement.
• He allowed only natural laws to shape this world.

I discovered that even without divine intervention, the world would still organize itself according to natural laws. The sun, stars, planets, and Earth would form as a result of these laws.

Context: This thought experiment underscores Descartes’ belief in the universality and consistency of natural laws—a view that laid the groundwork for modern physics.

Understanding Light, Fire, and Motion

I then applied these ideas to specific scientific questions.

• Light: I examined how light travels, reflects, and interacts with objects.
• Fire: I studied how fire produces heat and how different materials burn or transform under heat.
• Motion: I explored how objects move and interact, concluding that motion follows mechanical principles just like a clock.

The Circulation of the Blood

One of my most significant discoveries was an explanation of how the heart and blood circulation work.

• I observed that the heart is like a pump that moves blood through the body.
• The blood flows in a continuous cycle, moving through the arteries, capillaries, and veins.
• The heat in the heart causes blood to expand and contract, creating a rhythmic pulse.

This idea was similar to what the English physician William Harvey had recently proposed about blood circulation, but my explanation was based purely on mechanical principles.

Annotation: Descartes’ mechanistic view of the body—that living organisms function like machines—was revolutionary and influenced the development of modern biology and physiology.

Animals as Machines

Through these studies, I began to see that living bodies could be understood as complex machines operating under physical laws.

• Just as a clock or an automaton moves through mechanical parts, an animal’s body moves through nerves, muscles, and fluids.
• Animals do not need a soul to function—they simply follow natural biological mechanisms.
• Even without a "mind," animals could still perform all necessary functions, such as walking, eating, and breathing.

What Makes Humans Different?

I realized that if there were machines built to perfectly imitate an animal, we might never be able to tell the difference. However, if we tried to create a machine that imitated a human, we would always find two key differences:

• Language and Thought: No machine could ever use words or signs to express thoughts as we do. Even parrots and trained animals can mimic speech, but they don’t understand what they’re saying. Humans can respond intelligently to an infinite variety of situations, while machines and animals cannot.
• Reason and Adaptability: A machine might be able to perform some specific tasks better than a human. But it would fail in situations that require general intelligence and reasoning. Human minds are universal—we can learn and apply knowledge to new situations.

From this, I concluded that while the human body is a machine, the human mind (or soul) is something entirely different.

The Immortality of the Soul

Because the human mind is not part of the physical body, it is not affected by the death of the body.

• Unlike animals, humans have a rational soul that is distinct from the body.
• This means that the soul is immortal and continues to exist after the body dies.
• Understanding this truth is important because many people believe that humans and animals have the same kind of soul, leading them to ignore the afterlife.

By proving that human thought is independent of the body, I strengthened the argument for the immortality of the soul.

Annotation: This argument for dualism and the soul’s immortality has had a lasting influence on debates about mind, consciousness, and the afterlife.

Summary of Part 5

In this section, Descartes:

• Established that nature follows fixed laws that can be studied scientifically.
• Explained how blood circulates in the body through mechanical principles.
• Argued that animals are like machines, operating purely through biology without thought or reason.
• Showed that humans are different from animals because we have language, reason, and adaptability.
• Concluded that the human mind is separate from the body, meaning that the soul is immortal.

Part 6: Why I Delayed Publishing and My Vision for Science

Why I Hesitated to Publish My Work

I finished writing a book on these ideas three years ago and was about to publish it. However, I changed my mind when I heard that another scientist’s theory had been condemned by religious authorities.

Although I didn’t entirely agree with that theory, I saw nothing in it that threatened religion or society. This made me worry that some of my own ideas, even though based on reason and observation, might also be misunderstood or misinterpreted.

Rather than risk controversy, I decided to delay publication and continue my work privately.

Context: Descartes’ hesitation reflects the tense relationship between emerging scientific ideas and established religious or societal norms during his time.

Why My Research Matters

Despite my concerns, I still believed that my work had great value for humanity.

• My method had already helped me discover important truths in science.
• I believed that by continuing my research, I could help create a new philosophy based on practical knowledge rather than speculation.
• The ultimate goal was to improve human life through science and medicine.

I envisioned a world where:

• Instead of relying on abstract philosophy, we could develop a practical science to control and use nature’s forces.
• We could learn the laws of physics, medicine, and biology, and apply them to make life easier and healthier.
• Medicine, in particular, could eliminate many diseases and perhaps even slow down aging.

Annotation: Descartes foresaw a future where scientific progress would lead to significant improvements in human welfare—a vision that resonates with modern scientific aspirations.

The Need for Collaboration

I realized that one person alone could never conduct all the necessary experiments to confirm these ideas.

• Scientific progress depends on observation and experimentation, not just reasoning.
• To test my theories, I needed help from other scientists willing to conduct experiments and share their results.
• If enough researchers worked together, science could advance much faster.

This made me consider publishing my work, not just for personal recognition, but to invite others to contribute to this project.

The Importance of Starting with Simple Observations

In science, it is better to begin with common experiences rather than complicated experiments.

• When people try to invent new experiments without understanding basic principles, they often draw wrong conclusions.
• Instead, we should study the simple, natural events that happen around us and analyze them carefully.
• By first understanding basic causes, we can then move on to more complex phenomena.

I followed this approach in my own work:

• I started by looking for general laws of nature that govern everything in the universe.
• I then used those principles to explain specific things—such as the stars, the earth, water, fire, and air.
• Only after that did I move on to more detailed studies of biology and medicine.

By following this step-by-step approach, I found that almost everything in nature could be explained by a few simple principles. However, testing these explanations required many experiments, which I could not perform alone.

Why I Still Chose Not to Publish Everything

Despite my desire to share my work, I ultimately decided not to publish my full treatise on physics. Here’s why:

• I didn’t want distractions. Publishing my theories would lead to debates and controversies, which would take time away from my research.
• Scientific debates rarely lead to truth. Most debates are about winning arguments rather than finding the truth. Scholars often defend their own ideas rather than openly searching for new knowledge.
• My ideas were still developing. My research was still in its early stages. I believed that I was in the best position to develop these ideas further, rather than letting others misinterpret them.
• I had seen that when people try to repeat someone else’s ideas, they often distort them. This had already happened with ancient philosophers, whose true ideas were often misrepresented by later scholars.

The Role of Experimentation in Science

I realized that real progress in science depended on:

• Careful experimentation, not just logical reasoning.
• Testing hypotheses with real-world observations.
• Working together to collect and analyze results.

Since I couldn’t conduct every necessary experiment myself, I needed to find others who shared my vision and would help conduct scientific tests.

Why I Published This Discourse and Its Essays

Although I didn’t publish my full treatise, I did decide to publish this Discourse on the Method, along with some scientific essays (Optics, Meteorology, and Geometry). I did this for two reasons:

1. To prevent misunderstandings. People already knew I had been working on new ideas, and I didn’t want them to assume I had something to hide.
2. To encourage scientific progress. By sharing some of my discoveries, I hoped to inspire other scientists to conduct further research.

A Call for Open Scientific Discussion

I invite anyone who disagrees with my ideas to share their objections openly.

• If someone finds an error, I will gladly admit it.
• If a debate arises, I will explain my reasoning but will avoid endless arguments that lead nowhere.
• I encourage careful reading of my work. If anything seems strange at first, I ask that readers go through it carefully before rejecting it.

Final Thoughts on the Future of Science

Looking ahead, I plan to dedicate my life to the study of nature.

• I will focus mainly on medicine, as I believe it holds the greatest potential for improving human life.
• I reject any work that benefits some people by harming others—science should be used for good.
• My goal is not fame or fortune, but to contribute something truly valuable to the world.
• I do not seek recognition, and I prefer a peaceful life of study over any public honors. If my work is useful, that is enough for me.

Summary of Part 6

In this final section, Descartes:

• Explains why he hesitated to publish his full work, fearing controversy and misinterpretation.
• Describes his vision for science, emphasizing experiments, collaboration, and practical knowledge.
• Argues that the best way to study nature is to start with simple observations before moving to complex theories.
• Refuses to engage in endless debates, preferring to let his ideas be tested through real experiments.
• Chooses to publish this Discourse and some essays to encourage scientific progress without revealing everything at once.
• Commits to focusing on medicine, believing it can greatly improve human life.

Context: Descartes’ careful approach to publication and collaboration highlights his foresight in nurturing a community of inquiry—an approach that remains vital in modern science.

Conclusion

This concludes Descartes’ Discourse on the Method in contemporary English.

Through this work, Descartes:

• Develops a clear method for thinking logically and systematically.
• Lays the foundation for modern science and philosophy.
• Distinguishes the human mind from the body, arguing for the soul’s immortality.
• Advocates for an experimental approach to science, which later influenced the scientific revolution.

Final Note: Descartes’ rational and structured way of thinking remains one of the most important contributions to philosophy and science. His insistence on clear, methodical reasoning and his skepticism of unexamined tradition continue to inspire critical inquiry and intellectual progress today.