I'm a proponent of 了 as 'factuality marker' (that is it has nothing to do with 'perfectivity or completness of action'. See post: How exactly do time and "tense" work in Mandarin REALLY? for details about this theory.

Now, being what I'm, I've noticed second 'factuality marker' which acts almost exactly as 了. That marker is 是 in the 是...的 structure. There are couple of moments I would like to stress before the question:

  1. Contrary to implicit 了, 是 explicitly (by nature of literal translation) states it's nature as "factuality marker".
  2. As with 了, sentences with 是...的 tend to be translated in past tense.

The question: If 是...的 and 了 both render situation to facts, which in turn has correlation with being "in the past", what is the difference between them? Why have 2 'factualiy markers' (past tense markers by correlation).

Let's look at two senteces:

  1. 我们是今天早上打网球的

  2. 我们今天早上打网球了

What is the difference between them? Is there semantic difference? Can you give exaple when 是...的 can be used, but 了 can't?

  • Ummmmm, I must say 我们是今天早上打的网球 & 我们今天早上打了网球 sound more natural. Commented Nov 19, 2018 at 15:42
  • 我们是今天早上打网球的 is ambiguous. Think of this scenario: 球场门卫:你们看起来有点眼熟啊。 我:我们是今天早上打网球的,大爷你这就不记得了? Commented Nov 19, 2018 at 15:48
  • Sorry, I'm neither a Chinese native speaker nor an English one, but as far as I know (or think I do), the 是……的 structure enphasizes time, place, manner, etc. So, the difference between the 2 sentences would be: 我们今天早上打网球了 (we played tennis today in the morning) and 我们是今天早上打网球的 (we played tennis WAS today in the morning). Commented Nov 22, 2018 at 17:59

3 Answers 3


(今天早上) (打网球)[了]

"打网球" is the fact; "今天早上" is the relative phrase that indicate what time it happened. Remove the relative phrase "今天早上" and write "我们打网球了", the sentence is still a complete sentence. (we still know you've played tennis, just don't know when)

[] ([今天早上打网球) []

the entire phrase "今天早上打网球" is the fact

If you remove the relative phrase "今天早上" and write "我们是打网球的", the meaning would change completely. "我们是打网球的" means "we are people who play tennis"

The 'verb phrase' in [是]+ (verb phrase )+[的] structure is a single item that cannot be broke apart


The (verb phrase)+ [了] structure can be in any tense

[是]+ (verb phrase )+[的] structure can only be in past tense



"去美國" is the fact; 明天 is the relative phrase that indicate what time it will happen. Remove the relative phrase "明天" and write "他要去美國了", the sentence is still a complete sentence. (we still know you will go to American, just don't know when)


It is grammatically incorrect, because 要去美國 is not a face yet, not until tomorrow.

他(原定)(是) 明天要去美國(的)

It is grammatically correct, because 原定(originally planed) is a fact, and it happened in the past.

  • Thanks. Makes sence. But what would you say abour the difference of the original sentences (if we leave them as they are, not removing time adverbs)? Is there ANY whatsoever difference (except for stylistical one)?
    – coobit
    Commented Nov 19, 2018 at 12:21
  • Will this be an overkill to try to translate "他(是)明天去美國(的)" as "we became those who will travel US tommorow"? Although, yes, you are right (是...的) is literally "fact of present tense" but translated as "past tense" in some context.
    – coobit
    Commented Nov 19, 2018 at 12:27
  • 的 in "他(是)明天去美國(的)人" is an adjective marker that indicates "明天去美國" is an adjective for "人" - "what people? The people who will go to America tomorrow"
    – Tang Ho
    Commented Nov 19, 2018 at 12:29
  • So it would be better to translate "他(是)明天去美國(的)" as "We are(factual marker) the people who will travel US tommorow"... I see.
    – coobit
    Commented Nov 19, 2018 at 12:30

I'd say the two constructions are used in different contexts. See below example:

A: 你们什么时候打网球的?

B: 我们是今天早上打网球的

A: 你们今天早上做什么了?

B: 我们今天早上打网球了

I'm not quite behind the idea that 了 is 'factuality marker', while 是…的 is. 了 is an indicator of completion.

  • if 了 is completion then what RVC like 完 and many others do? ex. 吃完了. So it's verb+completion marker+another completion marker, just to make sure 吃 is absolutly complete :)
    – coobit
    Commented Nov 19, 2018 at 13:58
  • @coobit yes, 了 in 吃完了 denotes completion. It's like 吃过了. I actually take 完 as a verb and 了 as a complement.
    – dan
    Commented Nov 19, 2018 at 14:44
  • No one can say I didn't try to save you...
    – coobit
    Commented Nov 19, 2018 at 14:46
  • @coobit 吃完了 is clearly distinct from 吃过了.“'早餐吃过了?”“吃过了。”(“Did you have breakfast today?”“Yes.”)“早餐吃完了没有?我们要走了。”“马上吃完了,再等我一下。”(“Have you done your breakfast?We are leaving”“Almost done. Please wait a minute.”) They are not interchangeable here. Commented Nov 19, 2018 at 17:07
  • @coobit 吃完了 has another meaning. See: “我看你早餐买了那么多,吃完了没有啊?”“吃完了,我不会浪费的。”(“I saw you buying so much food for breakfast, have you eaten it all?”“Sure. I never waste food.”) Commented Nov 19, 2018 at 17:11

I feel that 是……的 is not an independent structure. I prefer to parse it as 是 (……的). 的 is actually a marker of the descriptive chunk before it, transforming it to (I am not sure of that jargon, but something adding 的 to form a noun phrase or else thing is very common). 是 express quality, feature, etc of the subject in a general sense. When I say general sense, I mean any description of the subject can be pushed after 是, and ……的 is not essential.






我:嗨!还不就是早上外面打球的! (弄坏玻璃的人是早上外面打球的)(Answer only the questioned part)




这些都是你臆想的!我可从没说过这种话。(Notice that here 是……的 is far from "factuality marker". 臆想 is my subjective judge.)


So it is clear that 是……的 is made of “判断动词” 是 and “名词化结构”……的, and it has nothing to do with "factuality marker ".

P.S. As to 了, things are quite complicated. 了 is neither "completion marker" nor "factuality marker". I ve read a quite informative article and I totally agree with the author's view.现代汉语“了”的语法意义的认知类型学解释

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