This book reviews the path of rationality through its intellectual developments, from the rationality of modernity to the rationality of the twentieth century, in a style that combines critical analysis and counter-argument. The book discusses the meaning of rationality and the concept of reason in Islamic and Western philosophy, then delves into the rationality of modern figures such as Descartes, Spinoza, and Leibniz, arriving at the rationality of the Age of Enlightenment with Immanuel Kant. It also addresses the cognitive transformations that resulted from the development of science in the thought of Karl Popper, Thomas Kuhn, and Imre Lakatos, attempting to answer fundamental questions about the relationship between rationality, religion, and science, and its fate in the dominance of European civilization.