Correction has a delivery protocol: "Begin with praise and honest appreciation," then "call attention to people's mistakes indirectly," then "talk about your own mistakes before criticizing the other person." The but-to-and swap is the precision instrument: "Many people begin their criticism with sincere praise followed by the word 'but' and ending with a critical statement... Once 'but' is used, the praise is canceled." Swap "but" for "and" and the praise survives the correction. Asking questions instead of giving orders completes the protocol — it makes the corrected person a collaborator in their own fix. And the smallest unit of the method: "Let the other person save face."

— In our words · Source: How to Win Friends and Influence People (Dale Carnegie)