If Everyone Did It, Would That Make the Act Wrong?

“What if everyone did that?” is often treated as a calculation of consequences: if everyone jumped the queue, the queue would collapse, so queue-jumping is wrong. Kant's universalisation test is stricter and more abstract. He says we should act only on a maxim that we can at the same time will as a universal law. The object of the test is not an isolated movement, but a maxim containing the situation, purpose and way of acting.

In the Groundwork of the Metaphysics of Morals, Kant considers a false promise. A person in need of money plans to borrow it by promising repayment without intending to repay. If “make a false promise whenever you need money” became a universal rule, promises would lose their credibility and the practice on which the deception relies would undermine itself. The problem is not merely an unpleasant outcome. The agent is quietly claiming an exception that others could not share.

Yet the question cannot mechanically decide every case. State the maxim too broadly and almost any act may be prohibited; state it too narrowly and a person can insert their name and date to escape the test. If everyone visited the same restaurant tonight it would be crowded, but dining out contains no internal contradiction. Kant scholars still dispute how maxims should be specified and how contradictions in conception differ from contradictions in willing.

My judgement is that universalisation is most useful for exposing reasons built on one-sided exceptions. Am I using a rule that I would refuse to let others use in the same way? It is a powerful consistency check, not a complete moral algorithm. Harm, rights, role-based duties and circumstances still require judgement. Passing the test does not automatically prove the whole act right.

https://plato.stanford.edu/entries/kant-moral/