What Bellarmine observed in connection with Galileo is both memorable and telling. “While experience tells us plainly that the earth is standing still,” Bellarmine wrote, nevertheless “if there were a real proof that the sun is in the center of the universe… and that the sun does not go round the earth but the earth round the sun, then we should have to proceed with great circumspection in explaining passages of scripture which appear to teach the contrary, and rather admit that we did not understand them than declare an opinion to be false which is proved to be true. But this is not a thing to be done in haste, and as for myself, I shall not believe that there are such proofs until they are shown to me.”

This is a model of sensible procedure. Bellarmine assumed that there could be no real conflict between nature and scripture, which is what Christianity has always taught. Consequently, he argued, if we have been reading scripture one way and the natural evidence shows that we were wrong, then we need to revise our interpretation of scripture and acknowledge our mistake. But first let us make sure that there is in fact conclusive scientific proof before we start changing scriptural interpretations that have been taught for a very long time. Bellarmine proposed a solution. Given the inconclusive evidence for the theory and the sensitivity of the religious issues involved, Galileo should not teach or promote heliocentrism. Galileo, a practicing Catholic who wanted to maintain his good standing with the church, agreed. Bellarmine issued an injunction and made a record of the proceeding that went into the church files.

For several years Galileo kept his word and continued his experiments and discussions without publicly advocating heliocentrism. Then he received the welcome news that Cardinal Maffeo Barberini had been named Pope Urban VIII. Barberini was a scientific “progressive,” having fought to prevent Copernicus’s work from being placed on the index of prohibited books. Equally significant, Barberini was a fan of Galileo and had even written a poem eulogizing him. Galileo was confident that now he could openly preach heliocentrism. But the new pope’s position on the subject was a complicated one. Urban VIII held that while science can make useful measurements and predictions about the universe, it cannot claim to have actual knowledge of reality known only to God. This theory, which sounds a bit strange, is actually quite close to what some physicists now believe, and as we shall see, it is entirely in line with Kant’s philosophical demonstration of the limits of reason.