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Principles of Philosophy was written by René Descartes and published in 1644. Descartes intended it to be his magnum opus—the synthesis of all his theories in physics and philosophy divided into four parts. Part I is the only part of the work that we, today, would call “philosophy.” It is an account of Descartes’s epistemology and his metaphysics. The other three parts of the work deal with Descartes’s natural philosophy, or what we would call “science.”

In the preface to Principles of Philosophy, Descartes explains why he felt the need to give a philosophical response to the new science in the first place. He writes that he views all of human knowledge as a tree—each part relying heavily on the others for vitality. The trunk of the tree he compares to physics, and the branches to the applied sciences of medicine, mechanics, and morals. He states that the roots, giving support and nourishment to the entire system, was metaphysics, the philosophical study of the nature of God, the world, and everything in it.

Descartes Principles of Philosophy intended as a coherent picture of the entire “tree” of human knowledge, which he hoped would serve as a textbook should his work ever be taught at the universities.

Read the overall summary, explanations of important quotes, and four Question & Answers about key ideas in Principles of Philosophy. Or, learn more by studying SparkNotes guides to other works by René Descartes.


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