Change of state with 了
了 at the END of a sentence signals a new situation — something is different now: 下雨了 "it's raining (it wasn't before)", 他二十岁了 "he's twenty now".
This is a different job from 了 right after a verb (completed action). Sentence-final 了 is about NOW vs. before. A very useful case: 不 + verb + 了 means "not anymore": 我不喝咖啡了 "I don't drink coffee anymore".
Examples
Related grammar points
Practice this pattern in graded stories like The Tired Old Engine (Part 3), The Child Who Forgot His Lunch (Part 2), The Proud Engines (Part 2) inside the Literate Chinese app.
