Letter to the Grand Duchess Christina

Galileo’s “Letter” attempts to do several things at the same time: to define scientific practice, to defend the validity of his discoveries, and to show that his discoveries aren’t sacrilegious. Galileo does all three by defining each idea in terms of the other. He argues that you can’t commit heresy by exploring truth because God creates the truth. The Bible doesn’t explore every aspect of the natural world. Evidence-based research doesn’t contradict the Bible because the Bible works in metaphor, not in literal truth.

Galileo’s arguments rely on the same theme. Scientific observation and scriptural analysis serve different purposes and uncover different aspects of the universe. He argues that we need to consider what the Bible says concerning particular ideas in different places, explore different metaphorical possibilities, and discuss the questions that those possibilities raise.

Galileo also explains that we can’t apply the Bible to natural phenomena and expect it to provide exact results. The Bible uses metaphor, so its descriptions of the natural world don’t correspond to how the world operates. The Bible doesn’t try to correspond to the natural world at all. He writes, “I would say here something that was heard from an ecclesiastic of the most eminent degree: ‘That the intention of the Holy Ghost is to teach us how one goes to heaven, not how heaven goes’” (Paragraph 13). It is our role to observe the natural world around us to understand it, not the Bible’s role to fill in the gaps in our knowledge. The natural world, in turn, can’t express truths about God and the universe in the same way as the Bible. We need both.

Galileo doesn’t simply argue in favor of heliocentrism, he also seeks to dismantle his foes. He argues that his detractors care about their reputation more than about truth; they are angry because he has shown they are wrong. He begins his letter by talking about what these people are like, writing,

But some, besides allegiance to their original error, possess I know not what fanciful interest in remaining hostile not so much toward the things in question as toward their discoverer. No longer being able to deny them, these men now take refuge in obstinate silence, but being more than ever exasperated by that which has pacified and quieted other men, they divert their thoughts to other fancies and seek new ways to damage me (Paragraph 2).

Galileo elaborates on this point throughout the “Letter,” clarifying what these new ways to damage him are. His detractors claim that he is sacrilegious and untrustworthy, and that he gratuitously misinterprets the Bible to suit his purposes. In other words, they claim that Galileo does what they are doing to him.

Galileo also argues that the Bible is written for ordinary people. The Bible discusses such complicated ideas that metaphor is the only way to explain them. It must also guide people toward spiritual truth and salvation. The Bible accomplishes both tasks. It uses metaphor to appeal to everyone, including people who believe that the Sun orbits the Earth because the Sun seems to move across the sky. It also uses metaphor to lead scholars and theologians toward a deeper truth. Galileo argues that his detractors offer the worst of both worlds. They misinterpret the Bible by taking it literally, and they do this to defend their reputations.