Immanuel Kant was an 18th-century German philosopher whose ideas have profoundly influenced the landscape of moral philosophy. His work represents a crucial moment in the Enlightenment, where reason began to take precedence over tradition, and he sought to establish a solid foundation for ethical theory grounded in rationality.

Kant’s most notable contribution to moral philosophy is the concept of the categorical imperative, which serves as a central tenet of his ethical framework. This principle can be understood as a universal moral law that applies to all rational beings, regardless of personal desires or situational contexts. In his seminal work, "Groundwork for the Metaphysics of Morals," Kant lays out the fundamental structure of his moral philosophy, establishing that genuine moral obligations are derived from reason rather than emotional responses or external consequences. This is a significant departure from consequentialist theories, which evaluate the morality of actions based on their outcomes.

Kant articulates multiple formulations of the categorical imperative, the most well-known being the principle that we should act only according to that maxim which we can at the same time will to become a universal law. At its core, this means that before we act, we should consider whether the rule guiding our actions could be applied universally to everyone. If a rule cannot be consistently universalized without contradiction, then it is not morally permissible. For instance, consider the act of lying. If lying were to be made a universal law, then trust would erode entirely, making the very act of lying itself impossible, as no one would believe anyone else. Thus, Kant argues that while lying may seem beneficial in a specific situation, it cannot be justified when viewed through the categorical imperative, which emphasizes duty and adherence to moral law over the pursuit of personal happiness.