Galileo Galilei's Argument Analysis

Salviati’s thesis in the excerpts of Galileo Galilei’s Dialogue Concerning the Two Chief World Systems, the second day, states that all motion is relative, and diurnal motion is simply relative to the earth, with an emphasis on Copernican heliocentrism. Salviati argues with propositions set forth by Simplicio and Sagredo concerning three questions, one in which the earth is movable or immovable, the second is whether there is a chance in making it movable, and lastly regarding what motion would occur. Salviati’s arguments are concerning his observations of the terrestrial motions which involves the diurnal motions, which he uses to support the heliocentric conception of heavenly motions.
To support his thesis Salviati states that it would be irrational for the celestial sphere to rotate around the terrestrial globe when considering the velocity needed to make the other
celestial bodies rotate. His evidence for the relativity of diurnal motion in relation to earth is provided in the example of the ship that is traveling with goods within it. He states that items which are equally moved are not capable of motion, this is where he compares the movement of an item relocated two inches across the ground compared to the ship sailing thousands of miles. He states that if an object on the boat is relocated one inch from its original location there would be more movement for the object than the thousands of miles it travels on the ship at sea. Salviati supports his thesis for the type of movement that occurs, by creating an order for the motion in which the planets rotate, he states that the larger circular orbit demands a longer revolution time. Saturn takes thirty years to complete an entire revolution and the shortest amount of time closest to earth is Jupiter which completes the rotation in forty-two hours.

The arguments that are proposed by Sagredo and Simplicio, range in consideration of motion and the purpose of diurnal motion.
Simplicio argues that the great motion is not emphasized or significant to other celestial bodies such as the sun, the moon, and how they rise and set, yet Salviati proposes that the characteristics mentioned would be meaningless without the earth. He argues that the changes occur simply in relation to the earth and are not in relation to the other heavenly bodies. In an argument about diurnal motion, Salviati states that Aristotle has no proof of this idea and that he simple states a reason without a valid demonstration on the topic of contrariety. Salviati poses his argument of the circular movement that the earth rotates from east to west and how the heavenly bodies move from west to east, creates circular motions that would be contrary to each other. Simplicio posed the argument on diurnal motion that is based upon Aristotelian theory, it is that circular motions are not contrary to one another, which he also argues that opposites cannot be defined as
contraries.
In Salviati’s arguments there were no references to religious views or theories to support his arguments. The emphasis was placed upon demonstrations such as shifts of night and day, and motion which is mentioned in the boat example, instead of written text. The context of each individual demonstration did not allude to religion in any form regardless of the individual presenting it. There was no mention of any religious ideas or morals from any of the three men, not a single religious fact was extracted from the excerpt. They could have been influenced by religion from their perspective but they did not use them as evidence or state them directly in the dialogues, therefore, religious views did not influence the dialogues.