已经【yǐjīng】

已经 means "already". It goes after the subject and before the verb, and the sentence usually closes with 了.

• × 已经我吃了 → 我已经吃了

The 了 says the situation has changed. 已经 adds that the change came sooner than expected, or sooner than the listener knew.

With a time, an age or a quantity

With a number, 已经…了 says a point has been reached.

In the negative

已经不…了 says something is no longer true. 已经没(有)…了 says something is no longer there.

"Not yet" is not the negative of 已经. It takes Huán还méi没.

• × 我已经没吃 → 我还没吃

Questions

Add 吗. The short answer drops 已经: 吃了.

已经 or 都

Dū都 before a time or an amount also means "already", with surprise or complaint attached. 都十点了 sounds impatient where 已经十点了 just reports.