This is a historian's book about what science is and does. Short and concise, and written at an introductory undergraduate level, it addresses broadly philosophical questions about the nature of science through an investigation of some key episodes in its past.

The book is divided into six short chapters, with an introduction, a conclusion, and a helpful bibliographical essay with suggestions for further reading. The chapters take us from the early seventeenth century up to the first part of the twentieth century, discussing examples taken from different sciences and different scientists. Chapter 1 (“The Mechanical Universe from Galileo to Newton”) begins with the mechanist universe of Descartes, Huygens, and Newton. (Despite the title, Galileo has little role to play in the discussion.) Peter Dear contrasts the mechanist conception of the world, as found in Descartes and Huygens, modeled on the machine—where everything is explained in terms of size, shape, and motion—with the Aristotelian conception modeled on the organism. The mechanist model, in turn, is contrasted with Newton's world of active forces.

In chapter 2 (“A Place for Everything: The Classification of the World”), Dear turns to taxonomic approaches to nature in the late seventeenth and early eighteenth centuries. Unsurprisingly, he treats the conflicts among different kinds of classificatory schemes for plants and animals in scientists such as Ray, Linnaeus, Buffon, Jussieu, and Cuvier. But in addition, he also discusses a taxonomic scheme proposed by Étienne François Geoffroy in 1718 for representing certain observed chemical facts about the reactions of metals in various solutions and William Herschel's scheme for classifying different kinds of celestial objects. Chapter 3 (“The Chemical Revolution Thwarted by Atoms”) deals with chemistry in the eighteenth century, focusing on the difference between the quantitative and phenomenological approach Lavoisier took, emphasizing exact observation and measurement, and the approach taken by Dalton, which emphasized physical models.

Chapter 4 (“Design and Disorder: The Origin of Species”) discusses Darwin's theory of natural selection, emphasizing how he transformed the notion of design in nature from the earlier natural history tradition. Chapter 5 (“Dynamical Explanation: The Aether and Victorian Machines”) deals with the use of mechanical models in nineteenth-century British physics. Dear discusses the way in which Victorian machines, particularly the steam engine, provided models for Faraday, Thomson, and Maxwell and the use of the concept of aether in their theories of electricity, magnetism, and light. Finally, in chapter 6 (“How to Understand Nature? Einstein, Bohr, and the Quantum Universe”), Dear treats the quantum revolution of the early twentieth century.

This is a very selective history of science that makes no pretense of completeness, nor could it be expected to do so in the roughly 150 pages that Dear devotes to telling his stories. Nor is there anything very surprising in the history itself. The originality of the account lies in the frame in which he presents the material, the conclusions about the nature of science that he draws from history.

Dear's claim is that science has two faces. On the one hand, it aims for a true representation of the way things really are and “is concerned with explaining and understanding the world” (2). Dear proposes reviving the old-fashioned term “natural philosophy” to capture this aspect of science. On the other hand, he emphasizes, “science is also about power over matter, and, indirectly, power over people” (2). This is what Dear often calls the instrumentality of science, the way in which science allows us to control nature rather than just describe it. On this conception of science, as Dear presents it, what is important about science is not the way it explains nature and allows us to understand it but simply the systematic description of experience that allows us to predict future experience. Illustrations of these two faces of science are woven through the historical chapters of the book. For example, in chapter 1, Dear contrasts Descartes’ use of mechanical models for understanding the phenomena of nature with Newton's use of active principles. But he also contrasts Descartes’ mechanism with Newton's more instrumental interest in simply systematizing the natural effects of gravity, without any pretense of having offered a causal explanation. In this case, Dear claims, Newton is seeking to merge instrumentality and natural philosophy: “Instrumentality could become natural philosophy, Newton hoped” (38). In his discussion of classification in chapter 2, Dear shows the way that classification can be used in two ways, either as a way of enabling us to control nature, as in the case of Geoffroy's table of chemical reactions, or as a reflection of the real relations among plants and animals, a reflection of God's plan in creation, as in Linnaeus's taxonomic program. This is also the contrast between Lavoisier's program in chemistry discussed in chapter 3, which sticks close to what can be observed and measured, and Dalton's atomic models of gases, which seek to give us a real understanding of what is going on in invisible nature. And, of course, the tension between instrumentality and the natural philosophical approach is what is behind the debates over the proper understanding of quantum physics discussed in chapter 6. Dear does not want to choose between the two faces of science: his claim is that while some scientists lean more in the one direction and others lean more in the other, both are an integral part of the scientific enterprise as it is found in history.

As his title would suggest, a key notion for Dear's conception of science is that of intelligibility. It is not altogether clear how the notion of intelligibility is related to the notions of natural philosophy and instrumentality that Dear emphasizes in his exposition. Intelligibility is most naturally associated with the natural philosophical aspect of science. At the beginning of his conclusion he writes, “This book has presented various examples of natural philosophy in the history of science. The hallmark of natural philosophy is its stress on intelligibility: it takes natural phenomena and tries to account for them in ways that not only hold together logically, but also rest on ideas and assumptions that seem right, that make sense; ideas that seem natural” (173).

Insofar as the natural philosophical is concerned with explaining and understanding, it seeks to make the world intelligible to us. But intelligibility can also attach to the instrumental for Dear. Talking about Bohr's interpretation of quantum mechanics, he notes, “In effect, he wanted to elevate the instrumental (here, predictive) effectiveness of quantum mechanics to the status of a kind of surrogate for intelligibility itself—just as much a hallmark of successful natural philosophy as intelligibility had often been in the past” (165). But this was not shared by all. As Dear goes on to remark, “And that was the ambition that Einstein wanted to thwart” (165).

What is most interesting about the notion of intelligibility, and perhaps most important for Dear, is the way in which what counts as intelligible is cultural and contextual:

Pulleys and levers were intelligible to Descartes and his contemporaries; the steam engines of the industrial world of the nineteenth century were intelligible to Faraday, Thomson, and Maxwell. Some physicists, such as Bohr, were able to let go of these kinds of models altogether and live in a world without causality, while others, like Einstein, demanded such standards of intelligibility. For others, the world is made sense of by putting things in organized lists. For others still, the idea of design and selection, artificial or natural, makes the world intelligible. What counts as intelligible is determined by cultural context and not by any abstract and universally compelling reasoning. And insofar as intelligibility is an ultimate goal of scientific activity, one can say that a central feature of science is also culturally driven. This, in any case, is what Dear gleans from the history of science.

There are some problems with the book. One can, as always, find factual mistakes or, at least, things about which one can quibble. My own main quarrel is with the treatment of the history of chemistry. In my own view, Dear oversimplifies the state of chemistry in the early eighteenth century and does not pay enough attention to recent trends in the historiography of chemistry that downplay the supposed distinction between chemistry and alchemy in the early modern period. But that is a controversial issue. Also, the brevity of Dear's exposition means that in some discussions it is not always easy to follow what is going on in the historical examples. For example, his account of Jussieu's scheme for categorizing plants is difficult to follow (57), as is his account of the polarization of light (122–23). Philosophers will be somewhat impatient with the inexactness of the opposition that he draws between natural philosophy and instrumentalities and the relation between this two-faced characterization of science and the notion of intelligibility that is central to the book: we analytic philosophers like things neater and cleaner. And finally, and most important, philosophers of science of a more realist bent will certainly want to address the final conclusion that Dear draws. While intelligibility may differ from culture to culture, time to time, and even person to person, one also wants to insist on the importance of the world in determining our scientific theories. Dear does not deny that the world has an important role to play in the game, but then he does not emphasize it either.

The book is intended for the general reader, to bring to the larger public some sense of what is currently going on in the history of science. But where it will succeed best, I think, is in the classroom. It is not detailed enough for a central text in either the history of science or the philosophy of science. But it is ideal as a supplementary text in the philosophy of science. It will do its job if it gets students curious enough about even some of the historical episodes that it treats to want to go out and investigate the details for themselves. And it will succeed if it undermines students’ (or professors’) naive confidence that there is a single, unambiguous answer to questions about the aim and goal of science and leads them to think more carefully about the still widely held view that the enterprise of science can be understood independently of cultural context. This book makes a good case for the continuing relevance of the history of science to the philosophy of science: if we want to know what science is, we need to know what it has been. And while this may not be Dear's point, it also argues for the continuing relevance of the philosophy of science to the history of science. The philosophy of science gives Dear the larger questions that he is addressing, as well as the tools that he uses to address them.