# CCI explained — Philosophical Works > Chapter companion for Philosophical Works by René Descartes. ## What happens Descartes argues that sensible bodies are composed of insensible particles, asserting that reason can extend beyond sensory perception. He uses the example of a tree's growth to illustrate that minute particles are added imperceptibly, and criticizes those who rely solely on the senses as the measure of knowledge. He advocates for explaining nature through analogy with observable phenomena rather than inventing obscure entities like substantial forms. ## Themes in this chapter ### Reason and Method Descartes emphasizes that reason can transcend sensory limitations, using analogy and rational inference to understand insensible particles. ### Critique of Traditional Philosophy He dismisses Scholastic concepts like 'first matter' and 'substantial forms' as obscure inventions that hinder true understanding of nature. ## Character check-ins ### René Descartes Author presenting the argument that bodies contain insensible particles and defending reason over sensory limits. ### Narrator First-person voice ('I', 'me') used to express the philosophical position. ## Key lines > But I allow many particles in each body that are perceived by none of our senses, and this will not perhaps be approved of by those who take the senses for the measure of the knowable. Descartes asserts that there are many particles in bodies that are too small to be sensed, which may be rejected by those who believe only what can be sensed is knowable. _Establishes the existence of insensible particles and challenges sensory empiricism._ > A tree increases daily, and it is impossible to conceive how it becomes greater than it was before, unless we at the same time conceive that some body is added to it. But who ever observed by the senses those small bodies that are in one day added to a tree while growing? Growth of a tree requires addition of matter, yet no one has ever seen the tiny particles added each day. _Uses a concrete example to argue for imperceptible particles._ > Nor do I think that anyone who makes use of his reason will deny that we philosophize with much greater truth when we judge of what takes place in those small bodies which are imperceptible from their minuteness only, after the analogy of what we see occurring in those we do perceive, than when we give an explanation of the same things by inventing I know not what novelties, that have no relation to the things we actually perceive, as first matter, substantial forms, and all that grand array of qualities which many are in the habit of supposing. Reasoning by analogy from observable phenomena to invisible particles yields truer philosophy than inventing unrelated Scholastic entities like first matter and substantial forms. _Advocates for mechanistic explanation over traditional Scholastic concepts._ ## Links - HTML: https://www.betterreads.online/discover/philosophical_works_se/chapters/cci - Book: https://www.betterreads.online/discover/philosophical_works_se - All chapters: https://www.betterreads.online/discover/philosophical_works_se/chapters