I. What is the change-of-state le了?
As a modal particle, the sentence-end le了 indicates that a new situation has emerged or a change has taken place. We often call this sentence-final modal particle ‘change-of-state le了’ or ‘new situation marker le了’. Compare the following sentences. One has a le了 at the end while the other does not. They convey different meanings.
1. Tiānqi rè le.
The weather has become hot.
This sentence implies that the weather was not hot before but now it has changed.
2. Tiānqi hěn rè.
The weather is hot.
Without the modal particle le了, the sentence simply announces the fact that the weather is hot.