To diagnose means to identify what's wrong by examining symptoms and evidence carefully. When a doctor diagnoses an illness, she looks at symptoms like fever or cough, asks questions about how you feel, and might run tests to figure out exactly what disease is causing the problem. A mechanic diagnoses car trouble by listening to strange noises, checking under the hood, and testing different systems until he discovers why the engine won't start.

The word comes from medical practice but applies anywhere you need to solve a problem systematically. A computer technician diagnoses software issues. A teacher might diagnose why a student struggles with reading. The key is gathering clues and using knowledge to identify the specific cause.

A diagnosis is the conclusion reached through this process. If a doctor's diagnosis is strep throat, that means she's determined the specific cause of your sore throat. Getting the right diagnosis matters because different problems need different solutions: you can't fix a flat tire by adding engine oil, and you can't cure strep throat with cough syrup.

Diagnosing requires both careful observation and expertise. Anyone can notice something's broken, but diagnosing why it's broken takes knowledge, experience, and methodical thinking.