Roger Bacon (1214-1294), also known as Doctor Mirabilis (Latin: "wonderful teacher"), was a philosopher who placed considerable emphasis on empiricism, and is thought of as one of the earliest advocates of the modern scientific method.
He met the Cardinal Guy le Gros de Foulques, who became interested in his ideas and asked him to produce a comprehensive treatise. Bacon, being constrained by a rule of the Franciscan order against publishing works out of the order without special permission, initially hesitated. The cardinal became Pope Clement IV and urged Bacon to ignore the prohibition and write the book in secret. Bacon complied and sent his work, the Opus Majus, to the pope in 1267. It was followed in the same year by the Opus Minus, a summary of the main thoughts from the first work. In 1268, he sent a third work, the Opus Tertium to the pope, who died the same year. Bacon fell out of favor, and was in fact later imprisoned by the Franciscan order, presumably because of some of his controversial teachings and aggressive style.
In his writings, Bacon calls for a reform of theological study. Less emphasis should be placed on minor philosophical distinctions as in scholasticism, but instead the bible itself should return to the center of attention and theologians should thoroughly study the languages in which their original sources were composed. He was fluent in several languages and lamented the corruption of the holy texts and the works of the Greek philosophers by numerous mistranslations and misinterpretations. Furthermore, he urged all theologians to study all sciences closely, and to add them to the normal university curriculum.
He rejected the blind following of prior authorities, both in theological and scientific study. His Opus Majus contains treatments of mathematics and optics, alchemy and the manufacture of gun powder, the positions and sizes of the celestial bodies, and anticipates later inventions such as microscopes, telescopes, spectacles, flying machines and steam ships. Bacon studied astrology and believed that the celestial bodies had an influence on the fate and mind of humans. He also wrote a criticism of the Julian calendar which was then still in use.
He was intimately acquainted with the philosophical and scientific insights of the Arabic world, which was the most advanced civilization at the time. He was an enthusiastic proponent and practician of the experimental method of acquiring knowledge about the world. He planned to publish a comprehensive encyclopedia, but only fragments ever appeared.