Using 了 about future events

Question

I've come across some sentences, in which the particle 了 is used about future events.

1. 晚上我们请他们去吃了北京烤鸭。
2. 下个月我就回美国去了。
3. 现在该去海关办你的事儿了。

I don't know what kind of 了 is this? Is it 了1, marking the completion or realization of an action. Or is it 了2, marking change of state. How should one translate such sentences?

Answer 1

Sentence 1 is not about future event, it happened in the past, it's 了1 here.

In sentence 2 is 了2, marking change of state: I'm going back to America next month.

Sentence 3 is about beginning of action: Now it's time to go to the customs and do your work.

Check out the Wiktionary definitions.

Answer 2

I looked up the "现代汉语词典".when 了 is used as an auxiliary verb , it has two main functions:

1.用在动词或形容词后面，表示动作或变化已经完成

2.用在句子的末尾或句中停顿的地方，表示变化或出现新的情况。

According to the dictionary,了 in the sentence 1 satisfies the grammar point 1, like your understanding, it marks the completion of an action.了 in the sentences 2 and 3 satisfy the grammar point 2, like your understanding, it marks a change of state.

Answer 3

This is some advice I got either here or some other Chinese forum, I found it very helpful.

了和过的区别

了和过都能用在动词后面。
了 有表示过去时，现在进行时，将来时的意思。
如：我去了一趟超市。（过去）
我睡觉了。（现在）
我到了给你打电话。（将来）
过 只表示过去发生的某些事情。不能表示现在时和将来时。
如：我去过中国。
了 和 过 的用法是非常相似的，希望你能慢慢体会，多多练习。(ง •_•)ง,加油

1. 晚上我们请他们去吃北京烤鸭。
   Tonight we will invite them to eat Beijing roast duck. (Yuck!)
2. 晚上我们请他们去吃了北京烤鸭。
   In the evening we invited them to eat Beijing roast duck. (Yuck!)
3. 下个月我就回美国去了。
   Next month I return to the States. (Kiss me while you still can!)
4. 现在该去海关办你的事儿了。
   You should go to customs now to complete the formalities.