In Fundamental Principles of the Metaphysic of Morals, Immanuel Kant lays the groundwork for his moral philosophy, positing that true morality springs not from external laws but from a universal law within each individual. Kant introduces the categorical imperative, a principle demanding actions be universally applicable, guiding ethical behavior beyond personal gain. This text challenges readers to examine the motives behind their actions, advocating for a life led by duty and rational moral principles.