Whether the Essence of a Body Consists in Extension

A short letter arguing that body must be more than extension, because bodies resist being moved.

by Gottfried Wilhelm Leibniz5 passages held

French, the original language

Original title: Lettre sur la question si l'essence du corps consiste dans l'étendue
First published: 1691(aged 45)
Original language: French

Overview

Many able people in 1691, Leibniz conceded, held that the whole essence of a body lies in its length, breadth and depth, as Descartes had taught. Answering a correspondent who had asked for his reasons, he printed his dissent in the Paris Journal des Sçavans on 18 June 1691, and named Pierre Nicole, the Port-Royal moralist, as another who was not satisfied. If a body were nothing but extension, extension alone would have to explain everything a body does. It cannot explain inertia. A body at rest resists being set moving, and the larger it is the more it slows a body that strikes it, whereas a merely geometrical body would let a moving one carry it along without any loss of speed. Something beyond geometry — force, the capacity to act and be acted on — must belong to matter. Leibniz added that he was persuaded everything in the physical world happens mechanically, but that the laws of motion themselves have a higher source than mathematics, and that seeing this would reconcile the devout to the new corpuscular philosophy. A reply in the same journal that July granted that a body made of extension alone would be indifferent to motion and rest. That, Leibniz answered in January 1693, was exactly what he wanted conceded.

Key concepts

What is the Cartesian view that body is extension?

Descartes’ teaching that the whole essence of a body lies in its length, breadth and depth. Many able people held it in 1691, Leibniz conceded, and his letter to the Paris Journal des Sçavans answered a correspondent who had asked for his reasons against it. He named Pierre Nicole, the Port-Royal moralist, as another who was not satisfied.

What does inertia mean in Leibniz’s argument?

A body’s resistance to being moved. A body at rest resists being set moving, and the larger it is the more it slows a body that strikes it. A merely geometrical body would let a moving one carry it along without any loss of speed, so extension alone cannot explain what every collision shows.

What does Leibniz mean by ‘force’ in this letter?

The capacity to act and be acted on, which must belong to matter in addition to its geometry. Force is what extension lacks: it accounts for resistance and for the laws of motion. Leibniz still held that everything physical happens mechanically, but traced those laws to a higher source than mathematics.

What did the reply of July 1691 concede?

That a body made of extension alone would be indifferent to motion and rest. A reply in the same journal granted this while defending the Cartesian side. Leibniz answered in January 1693 that this was exactly what he wanted conceded, since real bodies are not indifferent: they resist, and extension cannot explain why.

Themes of the book

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

Why a Body Is More Than Extension

Is a body nothing but length, breadth and depth, as Descartes taught? Leibniz points to something every collision shows: bodies resist being moved.

If a body were only extension, extension would have to explain everything a body does, and it cannot explain inertia. A body at rest resists being set moving, and the larger it is the more it slows the body that strikes it; a merely geometrical body would be carried along with no loss of speed. So something beyond geometry, force, the capacity to act and be acted on, must belong to matter. Leibniz still held that everything physical happens mechanically, but traced the laws of motion to a higher source than mathematics, and hoped this would reconcile the devout to the new corpuscular philosophy.

extension
force
inertia
collision
body
motion
mechanism
substance
philosophy of physics
mathematics
metaphysics
religion and science

Enter a dialogue

Within this work

passages held: 5
distinct concepts: 14
by passages held, corpus-wide: #834

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.

1684 Meditations on Knowledge, Truth, and Ideas (Meditationes de cognitione, veritate et ideis)
A journal article of 1684, written into the Arnauld–Malebranche quarrel over ideas; its grades of knowledge return in the Discourse on Metaphysics and the New Essays.
LA
1691 Whether the Essence of a Body Consists in Extension (Lettre sur la question si l'essence du corps consiste dans l'étendue) you are here FR
1695 New System of Nature (Système nouveau de la nature et de la communication des substances)
Leibniz's first public statement of his system, printed in Paris in 1695; his replies to Foucher and Bayle kept it in the journals until 1698.
FR
1698 On Nature Itself (De ipsa natura)
An answer to Johann Christoph Sturm in the Acta Eruditorum of 1698, defending forces inside created things and tying the dynamics to the metaphysics of substance.
LA
1710 Theodicy (Essais de Théodicée sur la bonté de Dieu, la liberté de l'homme et l'origine du mal)
Published anonymously at Amsterdam in 1710, it was the book by which the eighteenth century knew Leibniz, and the one Voltaire answered with Candide.
FR
1717 The Leibniz-Clarke Correspondence (Recueil des lettres entre Leibniz et Clarke)
Ten papers exchanged through the Princess of Wales in 1715–16, cut off by Leibniz's death and published by Clarke in 1717.
FR
1718 Principles of Nature and Grace, Based on Reason (Principes de la nature et de la grâce fondés en raison)
A companion summary from the same Vienna months as the Monadology, long mistaken for it and printed before it, in 1718.
FR
1720 Monadology (Monadologie)
Written in French in 1714, it was known for over a century only in German and Latin translation.
FR
1765 New Essays on Human Understanding (Nouveaux Essais sur l'entendement humain)
The book-length reply to Locke, written as a dialogue in 1703–04, withheld after Locke's death and first printed in 1765.
FR
1840 Discourse Touching the Method of Certitude and the Art of Discovery (Discours touchant la méthode de la certitude et l'art d'inventer)
A plea for royal patronage of the sciences, addressed to an unnamed king, apparently Louis XIV, setting out the method of certainty and art of discovery Leibniz pursued for decades.
FR
1840 On the Ultimate Origination of Things (De rerum originatione radicali)
A short Latin essay of 1697 on why there is a world at all, left in manuscript until 1840.
LA
1840 Reflections on the Doctrine of a Single Universal Spirit (Considérations sur la doctrine d'un Esprit Universel Unique)
A French essay written in 1702 at the Prussian queen's palace outside Berlin, and left unprinted until 1840.
FR
1846 Discourse on Metaphysics (Discours de métaphysique)
The opening statement of Leibniz's mature metaphysics, written early in 1686 and left unprinted until 1846.
FR
1846 The Leibniz-Arnauld Correspondence (Correspondance de Leibniz et d'Arnauld)
The exchange of 1686 to 1690 between Leibniz and Arnauld over the Discourse on Metaphysics, every letter carried by the Landgrave of Hessen-Rheinfels.
FR
1854 Refutation of Spinoza (Animadversiones ad Joh. Georg. Wachteri librum de recondita Hebraeorum philosophia)
Private Latin notes on Wachter's book about Spinoza and the Kabbalah, given their title by the French scholar who published them in 1854.
FR
1890 Tentamen Anagogicum: An Anagogical Essay in the Investigation of Causes (Essai anagogique dans la recherche des causes)
A French essay of about 1696, from the years of Leibniz's dynamics, defending final causes against the mechanical philosophers.
FR
1903 New Openings (Nouvelles Ouvertures)
Written in French in 1686, by the Academy edition's dating, and left in manuscript until Couturat printed it in 1903.
FR
1903 Preface to the General Science (Préface de la Science générale)
Probably from 1677, an unfinished preface to the universal language of reasoning, unprinted until 1903.
FR
1915 Confessio Philosophi (Confessio philosophi)
Leibniz's first developed theodicy, a Latin dialogue from his Paris years; revised after Steno's objections, its account of sin returns much changed in the Theodicy of 1710.
LA

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