The term probability can be used in two main senses. In the frequency interpretation, it is a limiting ratio in a sequence of repeatable events. In the Bayesian view, probability is a mental construct representing uncertainty. This book is about these two types of probability and investigates how, despite being adopted by scientists and statisticians in the eighteenth and nineteenth centuries, Bayesianism was discredited as a theory of scientific inference during the 1920s and 1930s. Through the examination of a dispute between two British scientists – Sir Harold Jeffreys (1891-) and Sir Ronald Aylmer Fisher(1890-1962), the author argues that a choice between the two interpretations is not forced by pure logic or the mathematics of the situation, but depends on the experiences and aims of the individuals involved. The book should be of interest to students and scientists interested in statistics and probability theories and to general readers with an interest in the history, sociology and philosophy of science. – Contents : Acknowledgements; – 1. Introduction; – 2. Probability up to the twentieth century; – 3. R. A. Fisher and statistical probability; – 4. Harold Jeffreys and inverse probability; – 5. The Fisher-Jeffreys exchange, 1932–1934; – 6. Probability during the 1930s; – 7. Epilogue and conclusions. – Appendices : Appendix 1, Sources for Chapter 2; Appendix 2, Bayesian Conditioning as a Model of Scientific Inference; Appendix 3, Abbreviations Used in the Footnotes. – Includes bibliographical references (p. 239-251) and index.