Descartes never had a direct problem with the Inquisition, but he was always afraid of Church authorities, and at the same time he wanted their approval. His book on cosmology and physics, which was in accord with both atomism and Copernicanism, was ready to publish, when he withdrew it after he heard of the Inquisition’s condemnation of Galileo. In 1637, Descartes published his Optics, Meteorology, and Geometry that was prefaced with Discourse on the Method of Rightly Conducting One’s Reason and Reaching the Truth in the Sciences (1637). Here, Descartes developed his “doctrine of clear and distinct ideas.” (An idea was clear if one could be sure about what the idea was, and distinct, if it was different from other ideas.)

He next published his Meditations on First Philosophy (1641), partly in response to criticism he had received on the The Discourse on Method (1637). The Discourse explained Descartes’ new way of deriving the first principles of the sciences from a few clear and distinct ideas. The Meditations was published with a set of objections and replies from his contemporaries (including Marin Mersenne (1588–1648), Thomas Hobbes [1588–1679], and Pierre Gassendi [1592–1655]), and it went to a second edition in 1642. It was a completely original work in its claims that it was possible to be certain about the nature of physical reality and the existence of God based on certainty about one’s own existence.

Descartes’ pre-publication discussions led to refinements in his position that related his ideas to the intellectual concerns of his peers. From these discussions, the Meditations became one of the most famous philosophical works. Philosophers still obsess about it in the twenty-first century!

Descartes became increasingly concerned about intellectual attacks on him by papal authorities. His friends thought that he exaggerated the personal and professional dangers of these attacks, but Descartes’ own ambition was tied up with his response to them. His thinking went to the heart of the Catholic Church’s use of skepticism to deny the findings of the new science that contradicted Church doctrine and scripture. It was Descartes’ hope that the Jesuits would approve his ideas in the Meditations and even use it as a textbook.

Descartes’ next publication was Principles of Philosophy (1644), which he believed would be a masterpiece that would gain the Church’s approval.