To affirm means to state positively that something is true or to express strong support for something. When a witness in court affirms their testimony, they're declaring that they're telling the truth. When you affirm a friend's idea for the science fair, you're telling them it's good and backing them up.

The word carries a sense of confidence and certainty. You don't affirm something you're unsure about. If your teacher asks whether you finished your homework and you affirm that you did, you're giving a clear, definite “yes.” Affirmation is the noun form: receiving affirmation means getting confirmation or support.

Affirm is stronger than simply agreeing. When a judge affirms a lower court's decision, she's officially confirming that it stands. When parents affirm their child's worth after a disappointment, they're reinforcing an important truth. The word suggests both declaring something true and standing firmly behind it, like planting a flag. An affirmative answer means “yes,” while the affirmative side in a debate argues in favor of the proposition.