Galileo, a Model of Rational Thinking?

Reasoned. Critical. Open-minded. Fair-minded. Judicious. These words characterize Galileo's defense of the heliocentric theory of Nicolaus Copernicus, according to Maurice Finocchiaro in his On Trial for Reason: Science, Religion, and Culture in the Galileo Affair (225-48). But the book overlooks technical details of the science of Galileo's time. These details matter. They make Galileo's defense less impressive. And thus, like several other recent books that touch on Galileo and the Catholic Church, On Trial for Reason creates a problem for understanding this famous "affair."

Finocchiaro has written extensively on Galileo. He has tracked down and translated into English many documents related to "The Galileo Affair." He knows well the characters of the Galileo story and what they had to say. On Trial relies heavily on Finocchiaro's previous work: its bibliography includes sixteen of his publications, ranging in date from 1980 to 2018, and its notes abound with citations of those works.

A particularly engaging section of this book is the last part of the third chapter and the first part of the fourth (69–96). Here Finocchiaro presents Galileo progressing in his view of heliocentrism. In 1597, Finocchiaro writes, Galileo has merely a "mathematical appreciation" of heliocentrism (71): "he obviously does not think that the Copernican arguments are conclusive or even strong enough to convince someone who, unlike [the astronomer Johannes] Kepler, is not already favorably inclined [73]." Thus Galileo "neither believed nor accepted Copernicanism as true. Indeed, as he confessed later, he was much more impressed by the observational astronomical objections against it, and deemed them to be strong and unanswerable [75]." But the telescope, which Galileo began using in 1609, changed that. By 1614 Galileo was strongly endorsing heliocentrism, labelling it as "certain" and "conclusive" (86).

Yet Galileo kept an open mind. He was willing to include, in his 1632 Dialogue on the Two Chief World Systems, Ptolemaic and Copernican, Pope Urban VIII's argument that divine omnipotence put certain knowledge of the universe beyond our reach. Galileo complied with the request to end the book with this argument, says Finocchiaro, and "such compliance reflected in part Galileo's readiness and willingness to be cooperative and accommodating. It also reflected his judgment and recognition that there was something right about the pope's favorite objection [126]."

The outcome of Galileo's reasoned, critical, open-minded, fair-minded, and judicious look at the evidence was, of course, that heliocentrism comes out on top. He provided "a robust confirmation of the theory [3]." His ways of thinking and searching for truth became "a model of rationality [11]," "a model of critical reasoning and critical thinking [248]. And thus over time he has properly come to be seen as having been tried by the Inquisition for the chief offense of making a "reasoned defense of Copernicanism," despite it having been declared false and contrary to scripture by Church officials, and that defense has come to be seen as his key contribution to what we now call the Copernican Revolution (257)—itself "the most important intellectual transformation in human history [225]." Finocchiaro states that he is not out to produce a hagiography of Galileo (258), but the Galileo of On Trial is nevertheless quite a guy.

Galileo could hardly be that guy portrayed in On Trial—who could? But understanding why Galileo was not quite that model of rationality, critical reasoning, and critical thinking requires wading...