How did Kant use the categorical imperative to judge whether an action is morally right?

Immanuel Kant’s categorical imperative serves as the supreme formal principle of his deontological ethics, providing a rational framework to judge the morality of an action regardless of personal desires or consequences.123

To determine if an action is morally right, Kant proposed that one must evaluate the "maxim" (the underlying principle or intention) of that action using two primary formulations:

• Universal Law: One must act only according to a maxim that one can simultaneously will to become a universal law. If a maxim, when universalized, leads to a logical contradiction or becomes self-defeating—such as the practice of making false promises—it is deemed immoral.124
• Humanity as an End: One must treat humanity, whether in oneself or others, always as an end and never merely as a means. This formulation emphasizes that individuals possess inherent worth and should not be used as tools to achieve other goals.241

For Kant, moral worth is found only when one acts out of duty for its own sake, rather than from inclination or desire.13