Key Concepts

Meditation Argument Explanation
Meditation I Doubt and the Deceiving God Descartes questions the reliability of sensory perception and proposes the idea of a deceiving God or an evil demon that could be tricking us into believing false things. This leads him to doubt the existence of everything except his own mind and the fact that he is a thinking being.
Meditation II The Cogito Argument Descartes arrives at the famous conclusion "I think, therefore I am" (cogito ergo sum). He reasons that even if he is being deceived, the very act of doubting proves that he exists as a thinking being. This becomes the foundation of his search for certainty.
Meditation III The Existence of God Descartes attempts to establish the existence of God by arguing that the idea of a perfect being must have been caused by a perfect being, i.e., God. He also argues that God, being perfect, cannot be a deceiver, and therefore our clear and distinct perceptions must be true.
Meditation IV Truth and Falsity Descartes distinguishes between the faculty of judgement (which can make mistakes) and the faculty of perception (which cannot be deceived when it comes to clear and distinct ideas). He argues that errors arise from the misuse of free will and not from God's deception.
Meditation V The Essence of Material Things Descartes argues that the essence of material things is extension, which can be grasped by the mind alone. He also introduces the distinction between the mind (res cogitans) and the body (res extensa), and argues for the real distinction between the two.
Meditation VI The Existence of Material Things Descartes attempts to prove the existence of material things by arguing that since God is not a deceiver, and since we have a clear and distinct idea of material things, they must exist. He also discusses the nature of the union between mind and body.

Quotes

Meditation Quote
Meditation I: Concerning Those Things That Can Be Called into Doubt "Some years ago I was struck by the large number of falsehoods that I had accepted as true in my childhood, and by the highly doubtful nature of the whole edifice that I had subsequently based on them."
Meditation II: Concerning the Nature of the Human Mind: That It Is Better Known Than the Body "I think, therefore I am."
Meditation III: Concerning God, That He Exists "I am certain that I am a thinking thing. Does it follow from this that I can be certain of anything else? Certainly, in the first place, I have ideas of certain things."
Meditation IV: Concerning the True and the False "Now, it is manifest by the natural light that all fraud and deception depend on some defect in the knowledge or power of the agent."
Meditation V: Concerning the Essence of Material Things, and Again Concerning God, That He Exists "Although all the contents of the idea of God were of my devising, this does not follow that God does not exist."
Meditation VI: Concerning the Existence of Material Things, and the Real Distinction between Mind and Body "It is certain that the idea of me is in my mind, so it must be examined what this idea is, and whether it has, at the very least, all that is required to represent a true and real being."

Contents

Chapter Summary
Meditation I: Concerning Those Things That Can Be Called into Doubt In this chapter, Descartes begins by discussing the unreliable nature of sensory knowledge. He introduces the method of systematic doubt, questioning the truth of everything to build a foundation of certainty. This includes the potential deception by a malevolent demon.
Meditation II: Concerning the Nature of the Human Mind: That It Is Better Known Than the Body Descartes concludes that while he can doubt sensory and bodily perceptions, he cannot doubt his own existence as a thinking entity. This is encapsulated in the famous phrase "Cogito, ergo sum" ("I think, therefore I am"). He then reflects on what this means for the knowledge of the mind.
Meditation III: Concerning God, That He Exists In this chapter, Descartes seeks to build upon his foundation of certainty. He presents arguments for the existence of God, primarily using the idea that the notion of a perfect being must have a cause, and this cause must be God Himself.
Meditation IV: Concerning the True and the False Having established the existence of a benevolent God, Descartes examines the nature of error. He concludes that error arises not from God's imperfection but from the misuse of human free will, which exceeds our understanding.
Meditation V: Concerning the Essence of Material Things, and Again Concerning God, That He Exists Descartes discusses the essence of material objects, stating that their essence is distinct from their existence. He further argues that because he can conceive of clear and distinct ideas of material things, particularly geometrical ones, these must be true. He also reiterates his proof of God's existence through the idea of a necessary, perfect being.
Meditation VI: Concerning the Existence of Material Things, and the Real Distinction between Mind and Body Descartes concludes by affirming the existence of the material world and the independence of the mind from the body. He reconciles the reliability of sensory experience with God's non-deceptive nature and clarifies the dualism of mind and body.