Rationalism

Descartes formulated his conception of philosophy in explicit opposition to the Scholastic Aristotelians' emphasis on sense-based experience. The Meditations are best understood as a series of cognitive exercises that train the meditator to discover truths about the world by the use of pure intellect, independent of the senses. Beginning by purging the self of intellectual preconceptions, by doubting all knowledge hitherto received through the senses, the meditator rebuilds knowledge, achieving clear and distinct ideas of the nature of the soul, God, and body.

The Meditations was not a complete system of philosophy; it only laid the foundation for Descartes's broader philosophical project. Descartes explains in a letter to his friend Marin Mersenne that "my little book on metaphysics contains all the foundations of my physics." The point of the Meditations was to reconceptualize the physical world as a realm of extension, governed by laws of motion, and therefore amenable to mathematical investigation. Descartes envisioned his physics very broadly, extending his view from celestial bodies to terrestrial bodies, the operations of animals, and the nature of the human being. He meant for his scientific project to culminate in the Principles of Philosophy, which remained unfinished, although the broad lines of Cartesian science may be derived from other works.

Although Descartes turned to philosophy (metaphysics) in order to ground science and thought that the only genuine knowledge that human beings could achieve derived from the intellect operating independently of the senses, he nevertheless retained an important place in science for the senses. General truths about body only specify the possible range of explanations of physical phenomena; in order to determine the particular explanations, one must appeal to sense experience. Cartesian rationalism remains limited to the most general truths about the universe.