Is 了 optional when a time word is present?

Question

In sentences that already have a point in time word that indicates that the event happened in the past, is 了 optional? Or could there be some additional meaning with it present? For instance:

我昨天去商店。

or

我昨天去了商店。

Since "yesterday" is included in the sentence, does 了 really add anything?

Edit:

I am not concerned with the end-of-sentence 了 in this question, only the aspect marker. Follow up question: Is it grammatically incorrect to say ”我昨天去商店“？ That is, it obviously happened in the past but i don't use 了。

Answer 1

I think Chinese textbooks should start their 了 sections with this:

1. 了 is not about time.
2. 了 is not about tense.
3. Goto 1.

You are only concerned with 了 as an the aspect marker, aka completed action 了, or perfect aspect 了, so:

"昨天去商店" and "昨天去了商店" are both valid verb phrases. The second one explicitly states that the action was completed, whereas the first one does not.

As other posters have mentioned, "我昨天去商店" isn't wrong, but it is incomplete as a sentence because it leaves that verb phrase hanging. It feels like "Yesterday I went to the shop and..." in English. It needs to carry on with more information, e.g. "我昨天去商店的时候发现鸡蛋都卖完了".

"我昨天去了商店" is a complete sentence.

It might be easiest to look at examples to get a better sense of this:

我们昨天卖了十个。 -> "We sold ten yesterday."

到了红绿灯，往左拐。 -> "When you get to the traffic lights, turn left."

你买了东西以后可以去银行取点现金吗？ -> "After you've bought the things could you go to the bank and get some cash out?" (notice this in the future, the action hasn't happened yet, but still uses 了)

My point is that 了 is not about tense or time. It's about whether an action is complete in the time frame we're talking about.

I think that this is the sort of issue that can't be resolved by reading textbooks or explanations online. It's got to be done through long-term exposure and practice, in my view.

Answer 2

Just to expand on Hugh’s answer a bit.

To understand what’s wrong with ‘我作天去商店.’ standing alone, we could translate it as ‘Yesterday I was going to the shop.’ Speaking English, if you said this and just stopped, the listener would think, well so what?

There are some verbs which are not used with 了 where a time phrase is enough to show past action. For example, stative verbs:

我上個月不忙. Last month I wasn’t busy.

Also equative verbs like 是:

小的時候他是我的朋友. He was my friend when we were kids.

And also with some regular verbs:

去年他住在北京. Last year he lived/was living in Beijing.

昨天我想家. Yesterday I was missing home.

But in all these cases, the action described is inherently incomplete. So Hugh is correct, it’s best to go verb by verb and get to know how frequently and in what situations each will be used for completed actions.

If you want another take on aspect, try studying Russian with its perfective/imperfective verb system. For a native speaker of English, it’s really hard to get your mind around.

Answer 3

“了” is a special character usually meaning "finished" or "something happen in the future", we can summarize these points:

1. For a verb that can be persistent, “了” means “begin to do something immediately on spoken” （usually SVO+了）：

妈妈，我做功课了；做完功课后我出去散步。(Mon, I'll start homeworking, then I'll walk outside).

However, if SV了+O（Subject+Verb+了+Object），mostly this means something happened：

Compare with: 妈妈，我做了功课。

2. For a verb that can NOT be persistent, "了" means a finished state：

他坐下了。 - He has sit down (implying that he's currently sitting).

他骨折了。 - He has had a fracture (implying that the fracture is still there).

树叶掉落了。 - Leaves have fallen (implying that they are still on the ground).

3）For a verb that can be persistent but intransitive，"了" means something happened or immediately happen (just depending on contexts):

他唱了。(He's sung/He's going to sing).

Answer 4

1.When "了" put the end of a sentence, that means something changed/be changing/be going to change. It can be used in the past, present and future. But usually there is "就" in the future tense. "就" is similar to "will". for example:

"昨天，我去学校了。" refers to "I went to school yesterday."

"现在，我去学校了。" refers to "I am going to school now."

"明天，我就去学校了。" refers to "I will go to school tomorrow."

2.When "了" follows a Verb, that means something had done. And it should only be used in the past tense.for instance:

"昨天，我去了学校。" refers to "I went to school yesterday."

3.If a sentence without a "了", that means doing something/be going to do something. And it could be used in the present tense and future tense. for example:

"你现在去哪里？-- 我现在去学校。" means "Where are you going now? -- I'm going to school now."

"你明天去哪里？-- 我明天去学校。" means "Where will you go tomorrow? -- I will go to school tomorrow."

Answer 5

Is it grammatically incorrect to say ”我昨天去商店“？

It is grammatically correct. Since the sentence already indicate past tense you don't have to use it.

In basic Chinese learning material it is common to avoid using le 了 to keep it simple. See the examples at http://www.dictall.com/indu57/08/5708187C16D.htm (maybe you can find some in one of your learning books to verify)

Since "yesterday" is included in the sentence, does 了 really add anything?

Depends on the context. Probably not in this example, but 了 can also be used to make a sentence sound more serious. For example when saying 谢谢 you can add 了 - "谢谢了" to indicate that you're sincerely grateful.

Note that I got this information from a long discussion with a Chinese friend - I've got no credible sources to link to. Hopefully someone else can contribute with a credible source.

Answer 6

Edit for your new question.

• 我昨天去商店。Normally when you said it without 了， this sentence does not stop, you'd like to continuous and introduce what you did in the shop.

• 我昨天去了商店。 That's end. I got the information, you have been to shop. You can continuous your topic or not, what ever.

Answer 7

了 is a special word.

There are 3 question have to ask first.

A. 了 is a verb or not?
B. If not, is there other verb in the sentence?
C. If so, 了 is after the verb? or in the end of the sentence?

Following your example,

了 is not a verb.
了 is after a verb,

There are 3 tense I know.

1. past tense

   我昨天去商店。
   

   This is not a complete sentence!

   People usually say that following something else.

   For example: 我昨天去商店，買了很多東西。

   You can simply say that, but it's weird.

   (You said that, then? What'd happened?)

   The special situation is when you are in a conversation:

   example 1:
   甲：我昨天去商店。(Yesterday, I went to the store.)
   乙：去幹嘛？(So?)
   甲：你猜！(You guess?)
   ......(a long conversation.)
   

   .

   example 2:
   甲：你昨天幹嘛？(What did you do yesterday?)
   乙：我昨天去商店。
   

   .

   我昨天去了商店。
   

   Same as non-了 sentence, but emphasize it like "already did".

2. present tense

   我現在去商店。
   

   Not a complete sentence! Same reason as past tense.

   But you can't use 了 in this sentence if you wanna say

   "I'm going to the store now."

   You may use 就 to emphasize it like "我現在就去商店。"

   我現在去了商店。
   

   I'm on my way to the store.

   It's present and use 了 to tell someone in the past I was doing this too,

   It's Present Continuous! Same meaning as "我正在去商店的路上".

3. future tense

   我明天去商店。
   

   This is not a complete sentence! Same as present-tense.

   我明天去了商店。
   

   It's weird, because 了 is past and 明天 is future, but may happen in a story of a book.