Function of 了 Completion of Action or Change of State

Question

Sometimes I find it hard to distinguish between

a) 了1 (completion of action) and

b) 了2 (change of state).

In the following examples, I couldn't find out what kind 了 it is?

1. 我不能和你一起去买自行车了.

   a) I couldn't come with you.

   b) (Now) I can't come with you. (Before I could).

2. 我爸爸昨天没有回家，我想我应该自己做了。

a) I should have done myself and completed this task.

b) (Now in this new situation) I have to do it myself. (Before my father used to help me)

3. 那匹马往咱们这儿跑来了，我觉得它跑得非常快。

   I have no idea about the function of 了 in this one.

4. 他们看见一个大黑熊走过来了。

   a) The bear came here.

   b) The bear started to come here. (Coming of bear is a new situation)

5. 往前走三分钟，就到八号楼了。

a) After three minutes, act of reaching will be completed.

b) After three minutes, you will start to reach.

Answer 1

Let's review the uses of 了:

I. Used after a verb to indicate perfective aspect (action completion). The pattern is V + 了 + object.

• 我吃了一個蘋果. ― I ate an apple. / I have eaten an apple.

II. Used at the end of a sentence to A) indicate a change of state, or B) to inform the beginning of an action.

• A) 他是大學生了. ― He has become a college student. / He is a college student now.

• B) 我走了. ― I'm leaving now.

Here are my opinions on your questions:

1. 我不能和你一起去买(自行车)了. (IIA)

b) I can't come with you to purchase the bicycle (now).

2. 我爸爸昨天没有回家，我想我应该自己做了。(IIA)

b) I think I have to do it myself (now).

3. 那匹马往咱们这儿跑来了. (IIB) [那匹马往咱们这儿跑了来.] (I)

That horse runs toward us

4. 他们看见一个大黑熊走过来了。(IIB) 他们看见一个大黑熊走了过来.

b) They see a black bear coming by.

5. 往前走三分钟，就到八号楼了。(IIB) 往前走三分钟，就到了八号楼.

b) After three minutes, you will then reach building 8.