Reviewed by: The Idea of Principles in Early Modern Thought: Interdisciplinary Perspectives ed. by Peter R. Anstey Daniel Schneider Peter R. Anstey, editor. The Idea of Principles in Early Modern Thought: Interdisciplinary Perspectives. New York: Routledge, 2017. Pp. xvi + 303. Cloth, $140.00. This book is a collection of essays that relate in some way to the notion of a principle as it appears in early modern thought. Essays by James Franklin, J. C. Campbell, Alberto Vanzo, Anstey, and William R. Newman provide a survey of the usage of principles within particular subjects: the principles of early modern mathematics, equity law, corpuscularism, and chemistry or alchemy, respectively. Other essays, by Kristen Walsh and Michael LeBuffe, clarify a particular early modern thinker's understanding and usage of the term 'principle.' Walsh's essay concerns Newton's usage and understanding of the term, while LeBuffe's concerns Spinoza's. Other essays, by Daniel Garber and Kiyoshi Shimokawa, clarify how an early modern thinker, or a pair of thinkers, understand and use a particular principle or set of principles to do philosophical work. Garber's essay considers Leibniz's principle of the equality of cause and effect, while Shimokawa's considers the principles that Grotius and Hume use in their accounts of the origin of justice and its relation to utility. Sophie Roux's essay (a wonderful example of the high level of scholarship found in this collection) examines disputes concerning, and contemporaneous to, the two comets of 1664, and shows the role principles played (and failed to play) in demarcating the positions within these disputes. Scholars looking for a sustained investigation into the idea of principles in the early modern period will be disappointed. This is not on account of any failure on the part of these authors, but rather on account of there being no such thing. As this collection makes clear, the early modern period reveals no single idea of principles. Indeed, the only attempt at offering a broad discussion of various early modern ideas of principles is in the excellent introduction by Anstey. Still, this collection succeeds in satisfying its description within this same introduction, namely, as a "preliminary sounding of the subject" (1) of the nature and role of principles in the early modern period. Of the essays offering a "sounding" of principles as they appear within a particular subject, James Franklin's insightful and fascinating "Early Modern Mathematical Principles and Symmetry Arguments" stands out as particularly useful. Franklin's survey of mathematical principles effectively illustrates a dominant early modern conception of mathematics as a science of quantity that yields deductive knowledge of the real world. Likewise, among the essays offering an analysis of particular thinkers' use of the term 'principle,' Kristen Walsh's essay "Principles in Newton's Natural Philosophy" stands out in its significance. Walsh argues persuasively that, in the Principia, Newton used the term 'principle' to signify the functional role of a proposition within his theories. Walsh argues that if, in the Principia, Newton describes a proposition as a principle, he does so because the proposition satisfies two conditions: one, it has been deduced from the phenomena, and two, it serves as a premise in further deductions. Walsh shows how these two simple constraints systematize Newton's otherwise unsystematic usage of 'principle' in the Principia. Walsh's essay is well argued, well researched, and important. Newton scholars will undoubtedly find it of interest. The essays in this collection are all solid works of scholarship. As a collection however, they do not fit together in a very useful way. On the one hand, it will be the rare scholar who can engage deeply with the material covered in each and every essay. On the other hand, it will be the rare researcher of early modern thought who does not find at least some essays in the collection to be of use. The collection would have benefited from a tightening of its theme or perhaps even a tightening of the approaches with which the essays address the theme. As it stands, this "preliminary sounding" of the study of early modern principles lacks a cohesive focus. But the quality of the essays shows that further volumes investigating principles...