The World (Descartes) - The Void and Particles in Nature

The Void and Particles in Nature

Before Descartes begins to describe his theories in physics, he introduces the reader to the idea that there is no relationship between our sensations and what creates these sensations, thereby casting doubt on the Aristotelian belief that such a relationship existed. Next he describes how fire is capable of breaking wood apart into its minuscule parts through the rapid motion of the particles of fire within the flames. This rapid motion of particles is what gives fire its heat, since Descartes claims heat is nothing more than just the motion of particles, and what causes it to produce light.

According to Descartes, the motion, or agitation, of these particles is what gives substances their properties (i.e. their fluidity and hardness). Fire is the most fluid and has enough energy to render most other bodies fluid whereas the particles of air lack the force necessary to do the same. Hard bodies have particles that are all equally hard to separate from the whole.

Based on his observations of how resistant nature is to a vacuum, Descartes deduced that all particles in nature are packed together such that there is no void or empty space in nature (however, Descartes makes it clear that he does not claim that a void cannot exist in nature, since he lacks the observations necessary to say this with certainty).

Descartes describes substances as consisting only of three elementary elements: fire, air and earth, from which the properties of any substance can be characterized by its composition of these elements, the size and arrangement of the particles in the substance, and the motion of its particles.