Philosophical Works · Chapter
Part II: Of the Principles of Material Things explained
Descartes establishes the certainty of material things through God's veracity, defines the essence of body as extension alone, and clarifies the nature of space, rarefaction, and the distinction between quantity and substance.
What happens
Descartes establishes the certainty of material things through God's veracity, defines the essence of body as extension alone, and clarifies the nature of space, rarefaction, and the distinction between quantity and substance.
Themes in this chapter
Existence of God
God's veracity is used to guarantee the existence of material things and the reliability of clear and distinct perceptions.
Mind-Body Dualism
The mind is distinct from body; the human body is closely united to the mind, but perceptions serve the composite whole, not objective truth.
Reason and Method
Descartes systematically strips away sensory qualities to identify extension as the sole essence of body, using clear and distinct ideas.
Characters to notice
- René Descartes
Author and primary voice; argues for the existence of material things and defines body as extension.
- God
Invoked as guarantor of truth; cannot be a deceiver, thus material things must exist as perceived clearly and distinctly.
- Narrator
The 'I' who doubts, perceives, and reasons through the principles of material things.
Key passages
“For we clearly conceive this matter as entirely distinct from God, and from ourselves, or our mind; and appear even clearly to discern that the idea of it is formed in us on occasion of objects existing out of our minds, to which it is in every respect similar. But since God cannot deceive us, for this is repugnant to his nature, as has been already remarked, we must unhesitatingly conclude that there exists a certain object extended in length, breadth, and thickness, and possessing all those properties which we clearly apprehend to belong to what is extended.”
We clearly understand that matter is separate from God and our mind, and that our idea of it comes from external objects. Because God is not a deceiver, we can be certain that extended objects exist.
Descartes uses God's veracity to prove the existence of material things.
“In this way we will discern that the nature of matter or body, considered in general, does not consist in its being hard, or ponderous, or coloured, or that which affects our senses in any other way, but simply in its being a substance extended in length, breadth, and depth.”
The essence of body is not hardness, weight, or color, but only extension in three dimensions.
Descartes identifies extension as the primary quality of matter.
“For quantity differs from extended substance, and number from what is numbered, not in reality but merely in our thought; so that, for example, we may consider the whole nature of a corporeal substance which is comprised in a space of ten feet, although we do not attend to this measure of ten feet, for the obvious reason that the thing conceived is of the same nature in any part of that space as in the whole;”
Quantity and number are not separate from substance; they are only conceptual distinctions we make in our thinking.
Descartes argues that extension and substance are identical in reality.