Discourse on Method

Chapter-by-chapter summary

The book has six parts and no chapter titles, so the labels below are short descriptions of each part. It is non-fiction, so there is nothing to spoil: the argument builds step by step, and knowing the route in advance makes it easier to follow.

Part 1: What Schooling Left Unanswered

Descartes opens with a gentle joke: everyone thinks they have enough good sense, so nobody asks for more. He concludes that people differ not in how much reason they have but in how they use it. He then describes his education at one of Europe’s best schools. He loved mathematics for its certainty, yet found most other subjects full of rival opinions and no firm ground. After school he stopped reading and went travelling, looking for what he could learn from the world and from his own thinking. This matters because the book is a personal story, not a rulebook. Descartes invites us to watch how one mind tried to repair itself.

Part 2: The Four Rules

Held up in Germany by winter during the wars of the time, Descartes spends a whole day alone in a warm room and thinks about method. He notices that a city planned by one architect is tidier than one that grew by accident, and that a plan made by one mind is often better than one stitched together by many. So he decides to rebuild his own beliefs from the ground, though he does not urge anyone else to do the same. Borrowing from geometry, he lists four rules: accept only what is clearly true, divide each problem into small parts, move from the simplest to the more complex, and review everything so nothing is missed. These rules are the heart of the book.

Part 3: A Temporary Code for Living

If you tear down your house to rebuild it, Descartes says, you need somewhere to live meanwhile. So he adopts a “provisional morality” of four maxims. First, obey the laws and customs of his country and follow moderate opinions. Second, act firmly once he has decided, like a traveller lost in a forest who keeps walking in one direction instead of wandering in circles. Third, try to change his own desires rather than the order of the world. Fourth, review the available occupations and conclude that the best use of his life is to cultivate reason. The point is that radical doubt is for the mind, not for daily conduct; he does not want to stop living while he thinks.

Part 4: “I Think, Therefore I Am”

Descartes now sets aside everything that can be doubted, including the senses, geometry proofs and even waking life, since dreams can feel real. But while he doubts, he must be thinking, and so he must exist. This first certainty, the cogito, becomes his foundation. He concludes that he is a thing whose whole nature is to think, and which does not depend on the body. Next he argues that his idea of a perfect being could not come from an imperfect one like himself, so God exists, and since God is not a deceiver, clear and distinct perceptions can be trusted. Readers often find the first step convincing and the later proofs harder; both are reasons the book is still taught.

Part 5: The Body as a Machine

Here Descartes turns to nature and summarises a larger work on physics that he had held back. He describes the heart and the movement of blood, agreeing with an English doctor that blood circulates but explaining the heart’s action differently, through heat. He then claims that animals are like machines, built of parts that need no soul to work. Human bodies could be explained the same way, he says, but two things separate us from any machine: we can use language flexibly to answer any question, and we can act with general reason in any situation. For him, that shows the human soul is more than the body. This part shows his hope that physics and medicine can be built on the same method.

Part 6: Why He Published, and What He Hoped For

In the last part Descartes explains why he held back his larger work: news that the Church had condemned Galileo’s view of the earth’s motion made him cautious. He decided to publish only some essays on optics, weather and geometry, with this Discourse as their preface. He also states his hope for the sciences: knowledge should be useful for life, health and comfort, making us, in his phrase, masters and possessors of nature. He admits one person cannot do all the experiments needed and asks readers for help. The ending shows a man who sees method as the start of a shared project, not a finished system.

Key people and terms

• René Descartes (1596–1650). French thinker, mathematician and scientist who tells the story in the first person. He lived for many years in the Dutch Republic, where the book was printed. He offers his own path as an example for readers to judge, not as an order to follow.
• The four rules. His method for reasoning: accept only what is evidently true, divide problems into parts, go from the simple to the complex, and review everything completely. The pattern is borrowed from the way geometers build long proofs one small step at a time.
• Methodical doubt. The decision to doubt everything that can be doubted in order to find something certain. It is a tool used once, for a purpose, and not a lasting mood of cynicism. The aim is to reach solid ground, after which the doubting stops.
• The cogito. The sentence “I think, therefore I am.” It is the one truth that survives every doubt, because doubting is itself thinking. It gives Descartes a starting point for the rest of the argument in Part 4.
• Clear and distinct ideas. His test for truth. An idea that appears so plainly and so sharply separated from others that the mind cannot doubt it counts as reliable. Mathematical proofs are the model he has in mind.
• Provisional morality. Four temporary rules for living while rethinking everything: follow custom and moderate opinion, act firmly once decided, change your wants before the world, and choose a life of studying. They keep daily life steady during the great rebuilding.
• God as guarantee. In Part 4, a perfect God who does not deceive becomes the reason clear and distinct ideas can be trusted. Without this step, Descartes feels, even a careful thinker could never fully close the door on doubt.
• Animal-machines and the soul. Part 5 treats animal bodies as machines, and says humans differ because they use language flexibly and reason in any situation. This claim helped set up the later debate about how mind and body relate.
• The three essays. The Dioptrics, the Meteorology and the Geometry, printed together with the Discourse in Leiden in 1637. They were meant to show the method at work, and the Discourse serves as their preface.

Writing about this book

The Discourse is a book for testing ideas, so a good report picks one idea and examines it rather than summarising all six parts. These questions can help you find your own angle.

• Which of your beliefs do you hold only because everyone around you does? What happens when you apply the four rules to it?
• How is Descartes’ doubt different from anxiety or cynicism?
• What would your own “provisional morality” look like while you rethink a big decision?
• Do you accept that animals are machines? What would you say to Descartes?
• Why might it matter that he wrote in French rather than Latin?

A simple structure is: explain the idea in your own words, test it on an example from your life or from school, then say where you agree and where you have doubts. If you write about the cogito, show the steps of doubt that lead to it. Keep quotations short and let your own thinking lead.