How did Kant use the universalization test to judge whether an action is moral?

Immanuel Kant’s moral philosophy centers on the categorical imperative, which serves as an absolute, unconditional rule for all rational beings. To determine if an action is moral, Kant proposed the universalization test, famously formulated as: "Act only on that maxim through which you can at the same time will that it should become a universal law".123

In this framework, a "maxim" is the personal principle or rule underlying an individual's action. To apply the test, one must ask whether they could consistently will that their maxim be adopted as a universal law of nature that everyone follows.14

• Logical Contradiction: If a maxim, when universalized, becomes self-defeating or logically inconsistent, it is immoral. For example, if everyone made false promises when it suited them, the very practice of promising would collapse, as no one would rely on them.14
• Practical Application: Kant argued that this test provides a formal, rational framework for morality, independent of personal desires or consequences.13

While this test is a cornerstone of his deontological ethics, critics note that it can be difficult to apply in complex situations where principles clash, as it may not always provide clear guidance outside of cases involving strict logical contradictions.14