Immanuel Kant is the greatest philosopher of the modern era, the founder of classical German philosophy. Kant's range of professional interests was unusually broad. He developed a theory of the origin of the solar system, studied earthquakes, and lectured on physics and geography. However, Kant's most important works, which truly revolutionized his thinking, are the so-called 'critical works.' 'The Critique of Practical Reason' was published in 1788. This is Kant's main moral and philosophical work. Starting from the concept of a universal moral law (the categorical imperative), Kant offers a strictly ethical justification for it. At the heart of this law lies the idea of ​​transcendental freedom, or personal freedom of will, which is inherent in man and is unthinkable without moral self-discipline. For, as the philosopher believed, only an absolutely voluntary act can be recognized as moral.