It is commonly known that Galileo Galilei, aside from being a great thinker in areas of science other than astronomy, was a supporter of Copernicus's heliocentric theory of the universe. Galileo received much criticism because of his support of this theory. Criticism of his support developed into persecution of he himself, with Church authorities commanding him to renounce his support of the Copernican theories. During this period of harassment, Galileo wrote an open letter to the Grand Duchess Christina. His letter was intended to defend his position and explain why he felt his critics were in error. In writing the letter, Galileo uses Saint Augustine's authority and knowledge to defend his support of Copernican theories and journey towards the "truth".
It can be seen from the beginning that Galileo is writing defensively in his letter. At the very beginning, he criticizes those who criticize him in order to neutralize their opinions. He openly condemns their close-mindedness by writing, "Showing a greater fondness for their own opinions than for truth . . ." (175). In doing this he succeeds in illustrating his critics" inability to see past what they feel is right and distinguish what is the truth. The "truth" is Galileo's central theme in his letter, and he wants to present to the world what is true and what is false. .
In order to find the truth he uses the writings and influence of Saint Augustine, a pillar of the Church in the minds of all Catholics. It is obvious that Galileo would use Saint Augustine for support, because no one in the Church or anywhere else would refute his writings. Augustine's theories in theology are very important to the basic thinking of the Catholic Church. Of course, the Church leaders were the principle persecutors of Galileo, so it is logical that Galileo would choose Augustine as an appropriate foundation for defending his beliefs. .
Not only does Galileo utilize Augustine for his historical prestige, but also for the fact that Augustine's writings do support Galileo's position.