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This book exhibits deep philosophical quandaries and intricacies of the historical development of science lying behind a simple and fundamental item of common sense in modern science, namely the composition of water as H 2 O. Three main phases of development are critically re-examined, covering the historical period from the 1760s to the 1860s: the Chemical Revolution (through which water first became recognized as a compound, not an element), early electrochemistry (by which water´s compound nature was confirmed), and early atomic chemistry (in which water started out as HO and became H 2 O). In each case, the author concludes that the empirical evidence available at the time was not decisive in settling the central debates and therefore the consensus that was reached was unjustified or at least premature. This leads to a significant re-examination of the realism question in the philosophy of science and a unique new advocacy for pluralism in science. Each chapter contains three layers, allowing readers to follow various parts of the book at their chosen level of depth and detail. The second major study in "complementary science", this book offers a rare combination of philosophy, history and science in a bid to improve scientific knowledge through history and philosophy of science.

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Introduction.- Water and the Chemical Revolution.- Piles of Confusion: the Mixed Blessing of Electrolysis.- HO or H 2 O?.-Evidence in Action (or, The Contextuality of Evidence).- Pluralism in Practice.- Realism in a Free Society.- Epilogue: Complementary Science Continued.

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From the reviews:

"The present book is Hasok Chang´s second book in History and Philosophy of Science. ... he takes the example of the discovery of the formula H 2 O for water. ... The jury were very impressed by the overall quality of the book. Excellent scholarly research underpins the historical part of the book, and Hasok Chang develops his philosophical theses with clear and rigorous argumentation. ... book will be much discussed in the coming years, and become a central text in the history and philosophy of science." (Fernando Gil International Prize, fernando-gil.org.pt, February, 2014)
"This book is an exemplary instance of a welcome contemporary trend to produce work that self-consciously attempts to integrate history and philosophy of science. ... The history is detailed, acute and informative and the philosophical views defended are challenging. The book is valuable and well worth reading both by those professionally involved in history and philosophy of science and more widely." (Alan Chalmers, Science & Education, October, 2012)

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