The Dialogue and the Inquisition
From 1624 to 1630 Galileo was intermittently at work on his book, which at the last moment he was instructed not to call ‘Dialogue on the Tides’ because that would stress a physical argument for motions of the earth. It was a reasonable instruction in view of the traditional astronomical meaning of treating planetary motions hypothetically only, and leaving all physical considerations out of account, so Galileo changed the title to Dialogue Concerning the Two Chief Systems of the World — Ptolemaic and Copernican.
The dialogue form had been chosen for various reasons, among which was the fact that during the sixteenth century that form had become very popular for books designed to educate the public. The master— pupil conversations that first appeared for such purposes tended to be dull catechisms, so Galileo's dialogue introduced in effect two experts who vied for the support of a third, uncommitted participant. Another reason for writing in dialogue form was that the author could detach himself from commitment to views that might be objectionable. One spokesman principally represented Galileo, who himself appeared in the book only as ‘our friend’, or ‘the Academician’, or the like, when he wished to assert his personal claim to or responsibility for certain things.
Galileo made his principal spokesman Filippo Salviati, who had died