To deduce means to figure something out by thinking logically about the clues and information you already have. When you deduce something, you're not guessing randomly: you're using facts to reach a conclusion that makes sense, like a detective solving a mystery.

If you walk into the kitchen and see an empty cookie jar, crumbs on the counter, and your little brother with chocolate on his face, you can deduce that he ate the cookies. You didn't see him do it, but the evidence points clearly to that conclusion. When Sherlock Holmes examines muddy footprints and a torn piece of fabric, he deduces where the suspect has been and what happened.

Scientists deduce things all the time. A paleontologist might deduce how a dinosaur moved by studying its fossilized bones. A doctor deduces what illness a patient has by considering their symptoms together.

The key to deduction is that each step follows logically from what you know. You start with facts, think carefully about what they mean together, and arrive at a conclusion that makes sense. People who are good at deducing things pay close attention to details and think about how pieces of information connect. Deduction is the noun form: “Through careful deduction, she figured out who took her pencil.”