The “Letter” reads more like a modern essay than a personal letter because it argues a set of points in detail and only occasionally directly speaks to its addressee. Galileo makes himself appealing and accessible, even charming, by presenting his letter as an informal conversation between equals rather than a lecture to his inferiors or a plea to his superiors. He wants his readers to be on his side because the stakes of his argument are so high.

Galileo uses a friendly, almost conspiratorial tone. He does this particularly when he disparages “the common people,” people whom he considers too stupid to understand the Bible as anything other than literally true. He creates a divide between “the common people” and “us,” and his “detractors” and “us.” Galileo thus creates a category of “us” that includes himself, Duchess Christina, the leaders of the Catholic Church, and anyone else who might read the letter. When he discusses the mistakes of the “common people” or his “detractors,” he implies that it’s only reasonable to disagree with them. We of course know better than they do, Galileo says, and you, readers, of course agree with me.

Galileo makes a political decision by addressing the letter to Duchess Christina.