Kant's first formulation of the categorical imperative, stating that one should act only according to maxims that could become universal laws. It requires that moral principles be universalizable without contradiction.
From Latin 'moralis' (relating to customs) and 'formula' (fixed form). Kant developed this concept in the 18th century as part of his systematic approach to ethics, drawing on the idea that moral laws must have the same universal character as natural laws.
This formula reveals why lying is wrong in a surprisingly logical way: if everyone lied whenever convenient, the very concept of truth-telling would collapse, making lying itself impossible! Kant showed that immoral acts are literally self-defeating when universalized.
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