Galileo and Descartes on Copernicanism and the cause of the tides

• Galileo and Descartes defended significantly different versions of Copernicanism.
• Galileo’s demonstration of Copernicanism was compromised by the details of his theory of the tides.
• Descartes attempt to accommodate the Church’s condemnation of Galileo also was compromised by his tidal theory.

Galileo and Descartes were on the front lines of the defense of Copernicanism against theological objections that took on special importance during the seventeenth century. Galileo attempted to overcome opposition to Copernicanism within the Catholic Church by offering a demonstration of this theory that appeals to the fact that the double motion of the earth is necessary as a cause of the tides. It turns out, however, that the details of Galileo's tidal theory compromise his demonstration. Far from attempting to provide a demonstration of the earth's motion, Descartes ultimately argued that his system is compatible with the determination of the Church that the earth is at rest. Nonetheless, Descartes's account of the cause of the tides creates difficulty for this argument.