The modal particle 了 (1)
In Chinese, 了 (le) comes at the end of a sentence, or at a slight pause inside it, and marks a change of state or a new situation.
A negative answer uses 没 (méi), and 了 is not put at the end.
What it means
……了
Meaning:
the state has changed
a new situation has come about
下雨了。
It has started raining.
Structure
下雨 + 了
rain + new situation
下雨rain
了marks the new situation
Before it was not raining; now it is.
十二点了，吃午饭吧。
It's twelve o'clock, let's have lunch.
Structure
十二点 + 了
twelve o'clock + new situation
十二点twelve o'clock
了marks the time reaching a new point
吃午饭吧let's have lunch
Here 了 says the time has moved on — it is now twelve.
The negative answer
If the answer is negative, 没 is used and no 了 appears at the end.
弟弟起床了吗？
Has your younger brother got up?
没起床呢。
Not up yet.
Structure
没 + 起床
negation + get up
没not yet
起床get up
呢marks the situation as still going on
This negative answer carries no 了.
The rule in short
When the state changes
……了
Examples:
下雨了。
It has started raining.
十二点了。
It's twelve o'clock.
The negative answer
没 + verb
No 了 at the end.
Example:
没起床呢。
Not up yet.