WorkRené Descartes

Selections from the Principles of Philosophy

Descartes's system arranged as a textbook: the metaphysics compressed, then a whole mechanical physics of matter, heavens and minerals, built to unseat Aristotle in the universities.

by René Descartes118 passages held

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First published: 1644(aged 48)
Original language: French

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Overview

Meant for the university classroom, the Principia philosophiae appeared in Latin in 1644, laid out in numbered articles across four parts and built to be the textbook that displaced Aristotle. Part I gives the metaphysics of the Meditations in brief; Parts II to IV set out a whole physics — matter and motion, the heavens, magnets and minerals — all of it mechanical, none of it leaning on the "forms" and "qualities" of the schools. Descartes reduces the physical world to extension in motion and derives its workings from a few laws, among them an early version of what would become the principle of inertia. A French translation followed in 1647 with a new prefatory letter to the reader. His physics was taught in the Netherlands, France, England and parts of Germany; then Rome placed his works on the Index of Forbidden Books in 1663, and Catholic institutions cooled on him, though French Cartesians like Rohault and Régis kept teaching it for another generation. Much of the detailed cosmology — the great vortices that were supposed to sweep the planets around their suns — was overtaken within Descartes's century by Newton. What lasts is the ambition made concrete: a single metaphysics of extended matter, turned outward and made to run an entire universe without appeal to purpose or to God's continual arranging.

Key concepts

What are the four parts of the Principles?

Part I gives the metaphysics of the Meditations in brief, the principles of human knowledge. Parts II, III and IV lay out a physics: the general principles of material things, then the visible universe or heavens, then the earth, covering matter, motion, magnets and minerals. The whole is arranged in short numbered articles, a teaching order Descartes hoped would make it the standard university text.

Why does Descartes say matter is the same as extension?

For Descartes the essence of body is extension, being spread out in length, breadth and depth, and nothing more. Solidity, weight and colour are not part of what matter is. From this identification two famous consequences follow: there can be no true vacuum, since empty space would still be extended and so would be matter, and there are no indivisible atoms, since any extended thing can in principle be divided.

What are Descartes's vortices?

His mechanical account of the heavens. Space is full, so motion must be circular, and the planets are carried around their suns on vast whirlpools, vortices, of fine invisible matter, like straws swept round in an eddy. It let Descartes explain the solar system without action at a distance or empty space. Newton's gravitation displaced it within Descartes's own century.

What law of motion does the Principles state?

Among its laws of nature is an early version of the principle of inertia: each thing, so far as it can, stays in the same state, and what is once in motion continues to move in a straight line until something deflects it. Descartes grounds these laws in God's constancy rather than in the bodies themselves, then derives the workings of his physics from them.

How does the Principles differ from the Meditations?

Where the Meditations argues, staging six days of solitary doubt to win each conclusion, the Principles teaches. Part I condenses that metaphysics into brisk articles, and Parts II to IV build outward into a full mechanical physics the Meditations never attempts. One is a proof designed for objectors; the other is a course of study, Descartes's bid to be the textbook of the universities.

Themes of the book

What this book returns to, gathered into themes and ordered by how much of the text each one occupies.

The system laid out to be taught

Could a whole philosophy be set down in numbered articles a student works through in order, from first certainties to the last mineral? Descartes built the Principles to replace Aristotle in the schools.

Part I compresses the metaphysics of the Meditations into a teaching order: begin by doubting once to clear away the prejudices lodged since childhood, reach the thinking self and the God who secures clear ideas, then define substance, mind and matter. Written as articles rather than as meditations, it trades the drama of solitary discovery for a scaffolding a beginner can climb. The aim was frankly institutional, a textbook to unseat the Aristotle taught everywhere, and for a generation Cartesians did teach it across Europe, until Rome placed his works on the Index in 1663 and Catholic schools cooled.

epistemology
metaphysics
substance
methodology
prejudice
certainty
mind-body dualism
perfection
error

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A universe of matter in motion

What is the physical world made of, if not the forms and qualities of the schools? Descartes answers: extension, nothing but stuff spread out in space, pushed and turned by a few laws of motion.

Parts II to IV build an entire physics from one idea, that matter just is extension, the same as space, so there can be no true vacuum and no atoms. From a handful of laws, among them an early statement of what becomes inertia, Descartes derives the heavens, magnets and minerals, sweeping the planets around their suns on great whirlpools of subtle matter, his vortices. No purpose steers any of it and God does not continually arrange it. Much of the detail, the vortices above all, Newton overturned within the century, but the ambition lasted: one world, run by matter and motion alone.

extension
mechanics
motion
matter
space
physics
perception
sensory perception

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Within this work

passages held: 118
distinct concepts: 276
by passages held, corpus-wide: #474

What this book thinks together

The wheel takes this book’s leading concepts and shows how often they come up together. The wider the band between two, the more of its passages speak of both. Among them, most often together: “extension” and “matter”.

Concept co-occurrence, strongest first 8 concepts, joined by 15 pairings. 85 pairings reach beyond these concepts and are not drawn.
Concept	Paired concept	Shared passages
extension	matter	9
certainty	epistemology	5
extension	metaphysics	5
extension	substance	5
matter	metaphysics	4
epistemology	error	3
epistemology	sensory perception	3
error	sensory perception	3
matter	substance	3
metaphysics	substance	3
certainty	sensory perception	2
certainty	error	1
certainty	substance	1
epistemology	extension	1
epistemology	matter	1

Works held

The author's work in order, this book marked in place. Your-language title first, the original beneath it where the two differ; side chips show which full texts are held.

1637 Discourse on the Method of Rightly Conducting One’s Reason and of Seeking Truth in the Sciences
The first of Descartes's books to reach print, and the only one he wrote in French for a general reader; it sketches in a few pages the metaphysics the Meditations would expand four years later in Latin.
EN
1641 Meditations on the First Philosophy: In Which the Existence of God and the Immortality of the Soul Are Demonstrated (Meditationes de prima philosophia)
Cast as six days of solitary meditation and issued in Latin with six sets of Objections and Replies, this is Descartes's central metaphysical work; it deepens into radical doubt the method the Discourse had only announced.
EN
1644 Selections from the Principles of Philosophy you are here EN

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