Reason is the ability to think logically, solve problems, and make good decisions by considering facts and evidence. When you use reason, you think through a situation carefully instead of just guessing or acting on emotion. If your friend is upset because she thinks everyone ignored her at lunch, you might use reason to point out that several people were absent that day and others were studying for a big test.

Reason helps us figure out cause and effect: why things happen and what might happen next. Scientists use reason to design experiments and understand results. Detectives use reason to solve mysteries by connecting clues. When you work through a tricky math problem step by step, you're using reason to find the answer.

The word also means a cause or explanation for something. If a teacher asks the reason you were late, she wants to know what caused your lateness. You might say, “The reason I'm late is that I missed my bus.”

People sometimes contrast reason with emotion or superstition. Using reason means basing your conclusions on evidence and logic rather than fear, wishful thinking, or assumptions.

As a verb, reason means to think in a logical way or to discuss something using logic. When two friends disagree about something, they might try to reason with each other by calmly sharing their perspectives and listening to the other's point of view. The goal isn't just to win the argument, but to find the truth together.