The Cambridge Companion to Galileo (review)

The contributions fall into three main areas: Galileo’s work on mechanics, his defense of Copernicus, and his relationship with the church. The relative number of pages devoted to these topics is unusual: the ratio is roughly 3 to 1 to 3.

The papers on Galileo’s mechanics and physics are by William Wallace, Peter Machamer, Rivka Feldhay, Wallace Hooper, and Pietro Redondi. Wallace concentrates on unpublished manuscripts from Galileo’s early period, arguing that they reveal Galileo’s intense involvement with Aristotelian philosophy. As in his other writings, Wallace emphasizes the importance of the demonstrative regressus argument for Galileo’s thought, especially for Galileo’s later claim in the Dialogue to have demonstrated the earth’s motion from the phenomenon of the tides. Machamer offers an “Archimedean” interpretation of Galileo, stressing the Galileo’s use of simple machines, especially the balance, as a model of intelligibility throughout his scientific work. According to Machamer, these machines functioned as something like a Kuhnian exemplar for Galileo, providing the element of necessity and picturability that Galileo deemed essential for scientific explanation. Feldhay explores the role of mathematics in Galileo’s science, arguing that Galileo began to diverge from the Jesuit-Aristotelian tradition once he gave up trying to understand the causes of accelerated motion and focused instead on its geometrical analysis in terms of degrees of velocity. In a useful discussion, Hooper follows the development of Galileo’s inertial mechanics, concluding that even in the Discourses (1638) it is unclear whether Galileo abandoned his pre-Newtonian notion of impetus as the sustaining cause of motion. Redondi examines the relationship of Galileo’s physics to his theology. While Redondi’s conclusion is clear—“Galileo’s physics required God”—his argument is hard to follow, ranging as it does over Galileo’s views on time, atomism, macroscopic and microscopic physics, and cosmogony.

Only two articles are directly about Galileo and the Copernican theory but those two pieces, by William Shea and Noel Swerdlow, are models of clarity. Swerdlow focuses on Galileo’s telescopic discoveries 1610–13 while Shea covers the entire period up to the Dialogue of 1632. Unfortunately, this involves repetition of the material about the telescopic discoveries, including some diagrams and illustrations. Tighter editorial control might have avoided this duplication and allowed Shea to devote more time to the fascinating arguments in the Dialogue. What we have is fine, but more would have been better.

On Galileo and the church, there are contributions from Ernan McMullin, Richard Blackwell and Marcello Pera. McMullin argues that the seeds of Galileo’s downfall in 1633 were sown in his Letter to the Grand Duchess Christina (1615) in which Galileo endorsed a theory of scriptural interpretation remarkably similar to that contained in Augustine’s commentary on Genesis. McMullin finds a tension in that theory between regarding Scripture and natural science as mutually irrelevant while at the same time giving science priority over the literal reading of Scripture if and only if a demonstration has been provided. Once the demonstration principle was adopted, Galileo’s task of defending the earth’s motion against biblical literalism in the Dialogue became hopeless. Blackwell asks whether there could be another Galileo case in light of the Vatican’s admission of error in 1992. His answer is “Yes.” Blackwell reminds us that while in 1616 it was the Copernican theory that been tried and found heretical, in 1633 the sole issue was Galileo’s obedience to church authority. In Blackwell’s view, there remains the potential for conflict between the church’s “logic of centralized authority” and the democratic, pluralistic methods that give legitimacy to science. Pera, too, concludes that the possibility of conflict remains as long as the church insists that there are truths of faith, necessary for salvation, and those doctrines also have a factual content amenable, at least in principle, to scientific investigation.

The book concludes with two pieces: a survey by Michael Segre of the evolution of Galileo’s...