Change of state with 了
了 gets called a lot of things. It’s a pretty tricky concept for foreigners to wrap their heads around, especially if they’re thinking of it in terms of “time” or “tense.”
了 is a change of state marker. If something goes from being a certain way to another way, you express that concept with 了.
|I’m going to Taiwan in early June.
|I understand now (I didn’t before).
|Confucius is coming.
In the second example, Confucius was previously somewhere else, not intending to come over. Now that he’s in the process of coming over, we mark that change with 了.
了 is used quite frequently to express a completed action or a past action, but you should never get in the habit of “translating” past tense with 了.
That’s because it also marks completed actions, particularly when you have simple subject-verb-object sentences.