30.4Crothersfinal © Scott Crothers. Informal Logic, Vol. 30, No. 4 (2010) pp. 493-497. Book Review Maurice A. Finocchiaro. 2010. Defending Copernicus and Galileo: Critical Reasoning in the Two Affairs. Bos- ton Studies in the Philosophy of Science Vol. 280. New York: Springer. (Pp. xlii, 1–350. Hardcover. ISBN: 978- 90-481-3200-3. US $139) In Defending Copernicus and Galileo, Maurice A. Finoc- chiaro offers a defense of Galileo against both the charges of his official trial and the charges of subsequent philosophers, historians, and theologians that extend until the present day. In doing so, Fi- nocchiaro displays the richness of the two Galileo affairs. The first affair consists of Galileo’s defense of Copernicanism from his ear- ly work in mechanics through his trial, and the second consists of the analysis and evaluation of the first affair in the four centuries since. The aims of the book are three. First, Finocchiaro aims to display the importance of critical reasoning—of offering argu- ments, developing objections, and responding to criticisms—in both affairs. Second, he aims to defend Galileo by showing that Galileo’s defense of Copernicanism is, though mistaken in some areas, more right than wrong and thus ultimately successful. Third, Finocchiaro aims to adopt Galileo’s approach to critical reasoning to defend Galileo from anti-Galilean criticisms that have emerged since the trial. This Galilean approach to argumentation is charac- terized as reasoned, critical, fair-minded, and open-minded. The ensuing defense of Galileo generates discussions of scientific rea- soning, epistemology, metaphysics, and theology. This great breadth of coverage along with the clarity that Finocchiaro brings to all of these issues makes Defending Copernicus and Galileo not only a significant contribution to Galileo scholarship but also an ideal point of entry to the field for the non-specialist. 
 After a careful preface and introduction that outline the au- thor’s aims in some detail, the book follows in two parts. Part I presents Galileo’s defense of Copernicus against a host of objec- tions to the geokinetic thesis that were known to Galileo. These objections include empirical concerns, worries from Aristotelian physics, and theological criticisms. Finocchiaro presents a careful analysis of these objections and Galileo’s own responses to them. Finocchiaro does not attempt to show that Galileo is flawless in his defense. Instead, he demonstrates that Copernicanism can be de- fended on the same general lines advanced by Galileo even if Gali- leo was mistaken on some of the specifics. Aside from treating his- torical and evaluative issues that arise from Galileo’s defense of Scott Crothers 494 Copernicanism, Part I includes: a concise introduction to the geo- static cosmology that is second to none (Ch. 2), the use of Galileo’s early assessment of Copernicanism to evaluate the claims of con- temporary philosophers of science about theory selection (Ch. 3), a discussion of the distinction between mathematical, physical, and physical-mathematical reasoning (Ch. 5), and a nuanced treatment of the complementary roles of reasoning, criticism, and instrumen- tation (Ch. 6). 
 The lengthy discussion of the objection to the geokinetic the- ory from “the extruding power of whirling” (p. 97) is perhaps the best example of Finocchiaro’s balanced approach to defending Co- pernicus and Galileo. The objection from the extruding power of whirling is based on what we now call centrifugal force. Objectors to the geokinetic theory claimed that if the earth were indeed rotat- ing, then there would be an extruding power tending to expel ob- jects from the surface of the earth. Since this extruding power was known to be proportional to linear velocity and since the linear ve- locity at the earth’s surface is very large, it was claimed that every object on earth would be flung into space. Since objects are stable on the earth’s surface, the earth must not be in motion. 
 Finocchiaro displays both the merits and mistakes of Galileo’s response to this objection. In short, Galileo acknowledges the truth of the conditional claim that if the earth we rotating, there would be an extruding power tending to expel objects from the surface to the earth. He even notes a weakness in the standard formulation of the objection and subsequently reformulates the objection to make it stronger than any that had previously been stated. In so doing Gali- leo exemplifies his fair and open-mindedness. To this clarification, Galileo adds three criticisms of the objection. First, he notes that this extruding power is opposed by the force which draws objects on the surface of the earth towards the earth’s center. Rather than carefully calculating the relative magnitudes of these forces, Gali- leo estimates that the extruding power is 1000 times weaker than its opposing force: a calculation later completed by Christian Huy- gens and Isaac Newton both of whom demonstrated that the gravi- tational force is 289 times that of the centrifugal force (p. 103). So though his estimation was off by nearly an order of magnitude, Ga- lileo’s criticism was essentially correct. 
 Galileo’s second criticism comes in the form of a geometric proof to show that no rotating sphere could rotate fast enough to expel objects from its surface. While critics regularly point to this proof as invalid, Finocchiaro notes a crucial ambiguity in the con- clusion of the proof which critics of Galileo have ignored. On one reading of the conclusion, the argument is invalid. On another, the argument is valid but not sufficient to refute the criticism from the extruding power of whirling. The geometric proof is flawed in ei- Review of: Defending Copernicus and Galileo 495 ther case. But this reasoned, critical, open-minded approach bears fruit by opening new lines of inquiry into Galileo’s defense of Co- pernicanism. 
 Finally, Galileo claims that the extruding power does not vary only with linear velocity as the initial objection assumes. He claims instead that the extruding power is also inversely proportional to the radius of the motion. Since the earth’s radius is so large, the extruding power is small even though the linear speed at the earth’s surface is significant. Here Galileo’s insights and oversights are clear. He is correct that linear speed is not the sole determinate of centrifugal force and thus his criticism of the objection from the extruding power of whirling is essentially correct. But Galileo in- correctly claims that the extruding power is proportional to the lin- ear speed divided by the radius. In fact, the centrifugal force is pro- portional to the linear speed squared and inversely proportional to the radius of motion. 
 Such a fair, critical, reasoned treatment of Galileo is a prime case of Finocchiaro employing the Galilean approach to critical reasoning. By laying all of the mistakes in Galileo’s arguments alongside his successes, we see that Galileo offers all the pieces necessary to successfully respond to the criticism from the extrud- ing power of whirling. Finocchiaro is thus successful not only in defending Galileo but also in demonstrating the fecundity of the Galilean approach to critical reasoning.
 In Part II of the book, Finocchiaro turns from Galileo’s de- fense of Copernicus to the defense of Galileo. This includes both the criticisms leveled at Galileo during his trial and the subsequent criticisms of historians, philosophers, scientists, and theologians that have emerged since Galileo’s conviction on vehement suspi- cion of heresy. Here Finocchiaro continues his efforts to show that Galileo can be defended from these criticisms and does so by em- ploying Galileo’s own reasoned, critical, open-minded, and fair- minded approach. Part II commences with a concise overview of the events of Galileo’s trial (Ch. 7) which is a prelude to the leng- thy historical survey of arguments and counter-arguments about Galileo’s trial which constitute the second Galileo affair (Ch. 8). The historical material here is vast and Finocchiaro does well to focus only on issues relevant for assessing four prominent criti- cisms of Galileo.
 The first of the four criticisms considered by Finocchiaro (Ch. 9) is that, though Galileo was correct in concluding that the geoki- netic hypothesis was true, he made substantial logical and meth- odological errors in defending this thesis and these errors were suf- ficient to warrant his condemnation by the Inquisition. Here Finoc- chiaro’s historical acumen yields its greatest rewards as he disam- biguates the formal charges brought against Galileo at trial and Scott Crothers 496 convincingly shows how proper understandings of the Dialogue Concerning the Two Chief World Systems and the Letter to Grand Duchess Christina reveal that, though Galileo did make several minor errors, his primary reasons for defending the geokinetic hy- pothesis were cogent and his scientific and theological methodolo- gies were justified. The second criticism considered is that Galileo was convicted because he used scripture to support the truth of an astronomical claim (Ch. 10). Finocchiaro labels this a “myth” and traces its ori- gin, spread, and development. This leads through a complex his- torical episode including forged letters and outright fabrications that were instrumental in convincing a sizable group of scholars that Galileo believed scripture authoritative on astronomical mat- ters when he maintained exactly the opposite. Pierre Duhem’s influential claim that the trial of Galileo was a tragic clash brought on by a faulty realist epistemology is the third criticism considered (Ch. 11). Duhem claimed that had Galileo been an instrumentalist—someone who believes that scientific theories are not attempts at true descriptions of reality but are in- stead useful formalisms for organizing phenomena—then he would never have asserted the truth of Copernicanism and would never have come under the scrutiny of the Inquisition. Here again Finoc- chiaro combines historical and philosophical prowess. He first shows how Duhem has conflated several important philosophical distinctions under his realism/instrumentalism distinction. Once the proper distinctions are made, Finocchiaro presents the relevant his- torical evidence to make clear that Galileo was not committed to an epistemology that both demanded and promised demonstrative cer- tainty to establish the truth of Copernicanism as is often claimed. The final criticism considered deals with the place of Galileo’s trial in the debates over the relationship between science and relig- ion (Ch. 12). The commitment to Galilean critical reasoning is as clear here as anywhere. The central targets include both Pope John Paul II and the philosopher of science Paul Feyerabend. The former claimed that the trial of Galileo is a case-study in the harmony be- tween science and religion and Galileo a hero for this cause while the latter offers a distinctive account of how science and religion came into conflict at Galileo’s trial. Finocchiaro is critical, fair, and open-minded in his approach to these competing claims. In John Paul II’s harmony thesis, Finocchiaro finds an accurate description of Galileo’s views but a dismissal of the hostility of many church leaders toward those views. In Feyerabend’s conflict thesis, Finoc- chiaro finds an historically untenable description of the trial but an example of the innovative turn in Galileo scholarship of the past century where less plausible views of earlier scholars are modified in ways which further illuminate both Galileo affairs. Review of: Defending Copernicus and Galileo 497 In summary, Maurice A. Finocchiaro’s Defending Copernicus and Galileo is a significant scholarly achievement. It is a model for historians of philosophy in that it combines historical erudition with penetrating philosophical analysis. Finocchiaro’s arguments are compelling, his writing lucid, and his coverage well-focused. This is material that philosophers of any specialization can find stimulating and it is handled in a manner that is, as intended, a fine example of reasoned, critical, fair-minded, and open-minded schol- arship. Scott Crothers St. Louis University