This book is the third of a three-volume set introducing the history of scientific thought (including social and human science). The area covered in this volume is Western Europe during the 18th and 19th centuries. Combining general descriptions with extensive excerpts from original sources in English translation, it concentrates on ways of thinking and actual argumentation and not just on results and mistakes; questions of validity are primarily dealt with in the perspective of the time of the writing, not on that of the 21st century. The work is of great interest to historians of science and culture, students as well as seasoned workers – but also for amateurs willing to invest the necessary serious efforts.