How did John Stuart Mill argue that utilitarianism supports honesty and promise-keeping?

John Stuart Mill argued that utilitarianism is compatible with moral principles like honesty and promise-keeping by rejecting the need to calculate the utility of every individual action.12

Instead of performing a new calculation before every decision, Mill proposed that individuals should be guided by general moral rules. He maintained that adherence to these principles—such as the requirement to keep one's promises—tends to increase overall happiness in the long run. By following these established rules, society maintains the trustworthiness and security necessary for human well-being.123

Mill’s approach suggests that while utility remains the ultimate standard, it is most effectively served by observing general principles rather than attempting to justify exceptions for every specific instance. Only under special, exceptional circumstances would it be necessary to consider whether a departure from these general rules is required.12