Galileo on the World Systems: A New Abridged Translation and Guide

Galileo Galilei, the great astronomer and physicist whose researches played so crucial a role in the history of science, also occupies an important place in the history of philosophy for his part in overthrowing the predominant Aristotelian concept of the nature of the universe. Galileo considered himself a philosopher and referred to himself as such on the title pages of his most influential works. Much recent research has been devoted to examining both the philosophical background of Galileo's scientific achievements and the philosophical implications of his scientific method. Born in Pisa, the eldest son of a famous music theorist, Galileo entered on the study of medicine at the University of Pisa but quickly shifted his interest to mathematics. From 1589 to 1592, he taught mathematics at Pisa while studying independently with Jacopo Mazzoni, a distinguished professor of philosophy. His earliest scientific works, directed against Aristotle's account of freely falling bodies, date from this period. In 1592 he moved to Padua, where he lectured on mathematics and astronomy, and by 1597 he was defending the Copernican helicocentric theory of the universe in a letter to his friend Mazzoni. When in 1609, he learned of the invention of the telescope in Holland, Galileo quickly designed an improved version of the instrument for his own astronomical observations. His startling discoveries---including the satellites of Jupiter---were revealed in 1610 in his Starry Messenger (Sidereus nuncius), which led to his appointment as mathematician and philosopher to the Grand Duke of Tuscany. On a visit to Rome in 1611, he demonstrated the power of his instrument and defended the Copernican worldview in learned circles. Church authorities were divided on the question of whether the Copernican theory was consistent with scriptural accounts of the cosmos, and Galileo's position was attacked on theological grounds. He defended himself eloquently in his famous Letter to the Grand Duchess Christina (1615), arguing for the independence of scientific inquiry from theological constraints. Nevertheless, in the following year, he was forbidden to hold or teach the Copernican view. Retiring to Florence to pursue his scientific researches, Galileo let the Copernican question lie until a new pope, Urban VIII, seemed to offer a more favorable reception to his views. In 1632 he brought out his great Dialogue Concerning the Two Chief World Systems, a presentation of the Ptolemaic-Aristotelian and Copernican systems heavily weighted in favor of the scientific superiority of the latter. In spite of the support of his Florentine and Roman friends, Galileo was tried and forced to recant his defense of helicocentrism under the threat of torture; the Dialogue was placed on the Index of Prohibited Books and its author sentenced to house arrest for life. Galileo's last years were spent in scientific investigations that culminated in the publication of his Discourses on Two New Sciences (1638). Galileo's legacy as a philosopher lies in his outspoken defense of the autonomy of scientific investigation from philosophical and theological authority, and his conviction that mathematical proofs can and should be sought in physical science, that celestial and terrestrial phenomena can be accounted for by a single set of scientific laws, and that scientific explanations cannot be divorced from direct empirical observation of phenomena.