Dialogue Concerning the Two Chief World Systems

Galileo’s Dialogue Concerning the Two Chief World Systems, published in the Italian city of Florence in 1632, is one of the most talked about books in the history of science. Using the dialogue form, a genre common in classical philosophical works, Galileo masterfully demonstrates the truth of the Copernican system over the Ptolemaic one, proving, for the first time, that the earth revolves around the sun. Its influence is immeasurable. The Dialogue is one of the most important scientific treatises ever written.

The book is written in the form of conversation between three characters: Salviati, a Copernican who speaks for Galileo himself; Sagredo, an open-minded gentleman who gradually comes to accept Salviati's arguments; and Simplicio, a defender of the Ptolemaic world-view, which represented the church position. Simplicio’s simplistic dogmatism falls to Salviati's keen insights. The dialogue form allowed Galileo to claim impartiality– he was "equally" presenting both views– although in fact, of course, he clearly weighted the dialogue toward the Copernican point of view. Galileo presented all the arguments (mostly based on his own telescopic discoveries) for the Copernican theory and against the traditional geocentric cosmology. Galileo was soon standing before the Inquisition, which found him guilty and ordered his house arrest.