Philosophical Works · Chapter
Part I: Of the Principles of Human Knowledge explained
Descartes establishes the method of radical doubt as the foundation for seeking truth, arguing that all previously held beliefs—including those from the senses and even mathematical demonstrations—must be doubted at least once in life.
What happens
Descartes establishes the method of radical doubt as the foundation for seeking truth, arguing that all previously held beliefs—including those from the senses and even mathematical demonstrations—must be doubted at least once in life. He identifies the first indubitable certainty as 'I think, therefore I am,' which reveals the mind as better known than the body. He then introduces the idea of God as a perfect being, uses it to prove God's existence, and argues that God's veracity guarantees the truth of clear and distinct perceptions. He distinguishes mind from body, identifies the essence of body as extension, and explains that error arises from the misuse of free will rather than from God. He concludes by advising that we rely on efficient rather than final causes and that we accept divine revelation even when it surpasses reason.
Themes in this chapter
Methodical Doubt
Descartes proposes a universal doubt of all things that admit even the smallest uncertainty, including sensory perceptions and mathematical truths, as a necessary step to find indubitable knowledge.
Cogito Ergo Sum (I Think, Therefore I Am)
The first certain knowledge discovered: while doubting everything, the very act of thinking proves one's own existence.
Characters to notice
- Narrator
The philosophical 'I' who undertakes the method of doubt and arrives at the cogito.
- René Descartes
The author and philosopher presenting his principles of human knowledge.
- God
The perfect being whose existence is proved and who serves as the guarantor of truth.
Key passages
“Accordingly, the knowledge, 'I think, therefore I am,' is the first and most certain that occurs to one who philosophizes orderly.”
The statement 'I think, therefore I am' is the foundational certainty for anyone who philosophizes in a systematic way.
This is the famous cogito argument, establishing self-existence as the first principle.
“We will also doubt of the other things we have before held as most certain, even of the demonstrations of mathematics, and of their principles which we have hitherto deemed self-evident; ... because we have learnt that God who created us is all-powerful; for we do not yet know whether perhaps it was his will to create us so that we are always deceived, even in the things we think we know best.”
We must even doubt mathematical truths because an all-powerful God could have made us systematically deceived about them.
Descartes extends doubt to mathematics by invoking the possibility of a deceiving God.
“But meanwhile, whoever in the end may be the author of our being, and however powerful and deceitful he may be, we are nevertheless conscious of a freedom, by which we can refrain from admitting to a place in our belief aught that is not manifestly certain and undoubted, and thus guard against ever being deceived.”
Regardless of whether a deceiving God exists, we have free will to withhold assent from anything uncertain, thereby avoiding error.
Free will is presented as the tool to avoid error by suspending judgment on doubtful matters.