The text to which Tufte references can be found here.
It is difficult to understand the gravity of the statement. It is one of the most profound and brave statements ever committed to text.
Consider the following context shamelessly taken from Wikipedia.
Western Christian biblical references Psalm 93:1, Psalm 96:10, and 1 Chronicles 16:30 include text stating that "the world is firmly established, it cannot be moved." In the same tradition, Psalm 104:5 says, "the LORD set the earth on its foundations; it can never be moved." Further, Ecclesiastes 1:5 states that "And the sun rises and sets and returns to its place, etc."The Church believed those passages to state that the earth is a stationary and immovable body.
The Church explained the sun to be a satellite that rotates around the earth, much like the moon.
The Church claimed to have absolute authority over scientific matters. The Church justified their positions on science ultimately through a literal interpretation of the Bible. Those who disagreed with the Church did so at risk of their lives and livelihoods.
What is Galileo saying in his statement. There are a two very important things.
- Galileo states that the strength of sound logic premised on observable visual evidence supersedes the authority of the Church.
- Galileo states that the strength of sound logic premised on observable visual evidence supersedes the authority of the Bible.
I can only imagine what bravery this took. Galileo must have considered and reconsidered his conclusion. One of Galileo's intelligence did not simply commit his refutation of the position of the Church to print without having absolute faith in his methods and his evidence.
In a sentence, Galileo declared that logic and observable reality are more credible than the Bible and the Church.
The Church, being one to not welcome some good constructive criticism banned Galileo's books, put him under house arrest, and forced Galileo to publicly recant his position and to state the geocentric position that the earth is a stationary object around which the other planets revolve.
I admire Galileo's bravery and hope that should I be faced with such a situation that I could muster the strength to do what is right.