Galileo Galilei (1564-1642) was born in Pisa, Italy February 18, 1564, the same year as William Shakespeare was born, and the same day Michelangelo died. When he was 18, he discovered the principle of the pendulum. At 22, he invented the hydrostatic balance. Perfecting his telescopes, he managed, in 1610, to discover four of the nine moons of Jupiter (the Galilean moons!), the rings of Saturn, and the phases of Venus!

He is most famous, of course, for the law of gravity, stating that two things of the same size and shape, but of different weights, will fall at the same speed through the same medium. That he demonstrated this by dropping things off the leaning tower of Pisa is probably a myth -- but who knows?

On the philosophical front, he was the first to make the distinction, which would become so important in English philosophy, between primary and secondary qualities. Primary qualities where physical properties of matter that could be measured, and therefore be made the subject of scientific analysis. Secondary qualities, on the other hand, were things that required the presence of a conscious, living creature: tastes, odors, colors, sounds... Only if these could be converted into primary qualities could they, he believed, become the subjects of science.

Galileo considered Copernicus’ theory as a proven fact, and taught it as such. The church, however, and especially the Jesuits, would only accept it if stated as a hypothesis, in the same way that some fundamentalists today will only tolerate the teaching of evolution if it is presented as just one theory among many.

Galileo pointed out to his critics that the Bible shouldn’t be read literally. If you do, you will end up with no end of absurdities and contradictions! It is meant to be taken metaphorically. Uh oh. Here are some quotes from a letter he wrote to the Grand Duchess Christina of Tuscany in 1615 :

...(N)othing physical which sense-experience sets before our eyes, or which necessary demonstrations prove to us, ought to be called in question (much less condemned) upon the testimony of Biblical passages which may have some different meaning beneath their works.

...I do not feel obliged to believe that that same God who has endowed us with sense, reason, and intellect has intended us to forgo their use.

(From p. 607 of Durant’s The Age of Reason Begins, and originally from Galileo’s Discoveries and Opinions, edited by Stillman Drake, pp 177 and 183)

For more from the same letter, click here.

In 1616, the Inquisition told Galileo to stop teaching Copernicus’ theory, and in fact condemned all publications and books, by any author, that did so. Galileo, probably recalling Bruno’s fate only 16 years earlier, quieted down. An essay by a student of his got things upset again, so Galileo spoke to the Pope himself. The Pope wouldn’t budge.

He finished his book on Copernicus’s theory anyway, but presented it as a hypothesis only, even putting it in the form of a dialog between supporters and detractors. Of course, naming the anti-Copernicus speaker "Simpleton" didn’t help. The Jesuits attacked it, even saying that Galileo was a greater danger to the church than Luther and Calvin. (They were probably, in the long run, right.)

At 68, he was, over four interrogations, threatened with torture (though not tortured), and asked to recant. He refused, a little less intensely each time. They pronounced him guilty of heresy. Eventually, he was put under house arrest, but otherwise free to teach and write. He was lucky.

Galileo died January 8, 1642. Science suffered quite a blow in the Catholic countries, with many scientists fearful of stating their views. This moved the center of scientific discovery to the Protestant North, not because Protestantism was more tolerant of science, but because the churches of those countries had less legal authority. In 1835, the church did finally take Galileo’s books off the banned books list. The church apologized in 1999.