I Theoretical Considerations Concerning Rationality and Scientific Change.- How Not to Talk About Conceptual Change in Science.- The Myth of the Framework.- A New View of Scientific Rationality.- Science, Protoscience, and Pseudoscience.- Methodology, Heuristics, and Rationality.- II Rational Scientific Changes.- Galileo and The Case of the Tides.- The Quest for Scientific Some Historical Considerations.- The Rationality of Galvani's Animal Electricity.- The Rationality of Entertainment and Pursuit.- Index of Names.