Mandarin Past Tense - the difference between adding "de" vs. adding "le"

Wǒ  chī  le     
     我     吃    了  
I ate.
vs.
(是)    wǒ  chī  de. 
(Shì)     我    吃    的. 
(It was)    I (who) ate. 

What's the difference between past tense form "le" and "de"?

The first sentence  我吃了 （wǒ chī le）is the simple past tense form meaning the action is complete.

The second sentence 我吃的（wǒ chī de）is the modifying form emphasizing another part of speech in the sentence. In this case, it means "I ate."  The emphasis is on "I" to mean "I am the person who ate it."  Actually, to be more clear about what is being emphasized, you should put 是 (shì) just before the part of the sentence that you want to emphasize. 

There's a good Mandarin Grammar Wiki explaining this classic "shi... de" construction. I'm repeating it here for convenience:

Using the "shi... de" construction

(Redirected from "Shi... de" construction)

• Level
  B1
• Similar to
  • Indicating purpose or intent using "shi...de" (B1)
  • Uses of "shi" with "de" (B1)
  • Using "de" (modal particle) (B1)
• Used for
  Emphasizing, Referring to the past
• Keywords
  是, 的

Also known as: 是⋯⋯的结构 (shì... de jiégòu), 是⋯⋯的 sentence and 是⋯⋯的 pattern.

The 是⋯⋯的 (shì... de) construction is used to draw particular attention to certain information in a sentence. It's often used to ask questions that seek specific information, or to explain a situation by emphasizing a particular detail. While not strictly tied to any "tense," the 是⋯⋯的 construction is frequently used when asking or telling details about the past.

Contents

 [hide] 

• 1 When to use it
• 2 Affirmative Form
  • 2.1 Structure
  • 2.2 Examples
• 3 Negative Form
  • 3.1 Examples
• 4 Used in a Question
  • 4.1 Examples
• 5 Where to put 的
  • 5.1 Examples
• 6 Completed Action
• 7 See also
• 8 Sources and Further Reading
  • 8.1 Books
  • 8.2 Websites

When to use it

Even if you understand that 了 is not used to mark "past tense" in Chinese, it's possible that you incorrectly use it that way sometimes. For example, what if you want to ask a question about something that happened in the past? Would you ever say one of the following sentences?

• 你 昨天 几点 到 了 ？Nǐ zuótiān jǐ diǎn dào le?What time did you arrive yesterday?
• 你 跟 谁 去 了 ？Nǐ gēn shéi qù le?Who did you go with?
• 他 用 什么 打 你 了 ？Tā yòng shénme dǎ nǐ le?What did he use to hit you?

In each of these sentences above, 了 is not the right choice, because you're not asking if an event happened or not. You're asking about details of past events. When you are singling out details for emphasis--in a question or a statement--you need to use the 是⋯⋯的 construction.
A 是⋯⋯的 construction can pick out any detail that's related to a past event. Whatever comes immediately after 是 is emphasized. Check out this example:

• A: 昨天 我 去 杭州 了。Zuótiān wǒ qù Hángzhōu le.I will go to Hangzhou tomorrow.
• B: 你 是 怎么 去 的 ？Nǐ shì zěnme qù de?How did you get there?
• A: 我 是 坐 火车 去 的 。Wǒ shì zuò huǒchē qù de.I went by train.

Now let's revisit those other three sentences and ask the questions correctly with 是⋯⋯的:

• 你 昨天 是 几点 到 的 ？Nǐ zuótiān shì jǐ diǎn dào de?What time did you arrive yesterday?
• 你 是 跟 谁 去 的 ？Nǐ shì gēn shéi qù de?Who did you go with?
• 他 是 用 什么 打 你 的 ？Tā shì yòng shénme dǎ nǐ de?What did he use to hit you?

Affirmative Form

是⋯⋯的 is not generally used for reporting new information, but for adding important details that make the information clearer. You could think of 是⋯⋯的 as being equivalent to saying one of the following in English:

• "The situation is that"
• "It's that... "
• "It was... that... "

Structure

Subj. + 是 + [Information to be Emphasized] + Verb + 的

This structure can be used to emphasize any detail, but most commonly it emphasizes time, manner, or place. Don't worry if this still seems a little confusing; lots of helpful examples are coming up!

Examples

• 你们 是 什么 时候 到 的 ？Emphasizing "when"Nǐmen shì shénme shíhou dào de?When did you arrive?
• 我们 是 昨天 到 的 。"Yesterday" is emphasized.Wǒmen shì zuótiān dào de.We arrived yesterday.

• 你 是 在 哪儿 出生 的 ？"Where" is emphasized.Nǐ shì zài nǎr chūshēng de?Where were you born?
• 我 是 在 中国 出生 的 。"In China" is emphasized.Wǒ shì zài Zhōngguó chūshēng de.I was born in China.

Although this structure is called the 是⋯⋯的 construction, the 是 is nearly always optional. You will often hear this structure with 是 omitted, so be aware. The only time 是 is required in this construction is when it's being negated. Other than that, 是 is commonly omitted.

• 你 骑 自行车 来 的 吗 ？Emphasizing "by bike"Nǐ qí zìxíngchē lái de ma?Did you come by bike?
• 我 走 来 的 。Emphasizing "by foot"Wǒ zǒu lái de.I came by foot.

• 谁 告诉 你 的 ？Emphasizing "who"Shéi gàosu nǐ de?Who was it that told you?
• 一 个 同事 告诉 我 的 。Emphasizing "a colleague"Yī gè tóngshì gàosu wǒ de.It was a colleague that told me.

You might be wondering, "can I still say the same thing without the 是 and the 的?" The answer is that in most cases, no, not really. While the 是 can sometimes be dropped, these examples sound weird without the 的. It's just a part of learning to ask questions naturally in Mandarin. You don't have to learn a "past tense," but you do have to learn this way of asking for details about the past, sooner or later.

Negative Form

是⋯⋯的 sentences can only be negated with 不, as 没 can not be used to negate 是.
是 can't be omitted in this construction because it's being negated.

Examples

• 我 不 是 走 来 的 。Wǒ bù shì zǒu lái de.I didn't come by foot.
• 他 不 是 跟 我们 一起 去 的 。Tā bù shì gēn wǒmen yīqǐ qù de.He didn't go together with us.
• 他们 不 是 在 网上 认识 的 。Tāmen bù shì zài wǎngshàng rènshi de.They didn't meet online.

Note that negating a 是⋯⋯的 construction creates the implication that the action in the sentence was carried out, and only the detail emphasized by 是⋯⋯的 is being denied. So, in the second sentence, the implication is that 他 didn't go with 我们, but did go out with someone. So negative 是⋯⋯的 constructions would work nicely in the final scenes of detective dramas.

Used in a Question

是⋯⋯的 constructions can be made into questions in the usual three ways to form questions in Chinese:

• With a question particle
• Within affirmative-negative questions
• With a question word

Examples

• 你们 是 不 是 去年 认识 的 ？Nǐmen shì bu shì qùnián rènshi de?Did you meet each other last year?
• 这个 东西 多少钱 买 的 ？Zhège dōngxi duōshǎo qián mǎi de?How much did this thing cost?
• 她 用 邮件 回复 的 吗 ？Tā yòng yóujiàn huífù de ma?Did she reply by email?

Where to put 的

Up till now we've said that 的 appears at the end of the sentence in a 是⋯⋯的 construction. This is very often the case. However, if there's an object, 的 can appear before the object.

Examples

• 我们 用 Skype 开 的 会 。the 的 comes before the object 会Wǒmen yòng Skype kāi de huì.We had a meeting by Skype.
• 谁 开 的 空调 ？the 的 comes before the object 空调Shéi kāi de kōngtiáo?Who turned on the air conditioner?

Note that if the object is a person, 的 has to go at the end of the sentence. Otherwise it can go before the object or at the end of the sentence.

• 我 是 在 图书馆 认识 的 我 男朋友 。I met my boyfriend in the library.
• 我 是 在 图书馆 认识 我 男朋友 的 。Wǒ shì zài túshūguǎn rènshi wǒ nánpéngyou de.It was in the library that I met my boyfriend.

• 你 是 昨天 见 的 客户 吗 ？I met my boyfriend in a cafe.
• 你 是 昨天 见 客户 的 吗 ？Nǐ shì zuótiān jiàn kèhù de ma?Is it yesterday you had a meeting with the client?

Completed Action

It's important to note that a 是⋯⋯的 construction also indicates that an action has been completed. However, this is not the purpose of a 是⋯⋯的 construction. The association with a completed action is more like a side effect of 是⋯⋯的. This means you shouldn't use 是⋯⋯的 just to indicate that an action is completed. Use the aspect particle 了 for that. Instead, use 是⋯⋯的 to draw attention to particular features of the action.

See also

• 的 (modal particle)
• Adding emphasis with "jiushi"
• Uses of "shi" with "de"
• Indicating purpose or intent using "shi...de"

More examples

If someone asks you, "Did you eat?" (你吃了吗?） you will say 我吃了(wǒ chī le).

If someone asks you, "Who ate the cake?" (谁吃的蛋糕？）you will respond with a  是⋯⋯的 (shì... de) construct (是) 我吃的.  [ (shì) wǒ chī de].  (It was) I (who) ate (the cake).

Let's look at a more complicated one:我昨天看了 （wǒ zuótiān kàn le）( I saw yesterday) 
我昨天看的 （wǒ zuótiān kàn de）(I saw yesterday) 

In a more complex sentence like above, "de" ending can be used to emphasize any part of the speech other than the verb. 

Question: 
Did you see it yesterday? （你昨天看了吗？Nǐ zuótiān kànle ma）
Answer:
I saw it yesterday. (我昨天看了。 wǒ zuótiān kàn le）

Question: 

Who saw it yesterday?

(是) 谁昨天看的？

(Shì) shéi zuótiān kàn de?

Answer:

​I saw it yesterday.  (我昨天看的。wǒ zuótiān kàn de）

Question：

Which day did you see it?

你 (是) 哪天看的? 

Nǐ (shì) nǎ tiān kàn de  

Answer:

I saw it yesterday.

我  (是)  昨天看的。

Wǒ (shì) zuótiān kàn de.

Another example: 
我去了
Wǒ qù le
I went. 

​我(是)走路去的
Wǒ (shì) zǒu lù qù de
I, by walking, went.

The second emphasize on the "how," not the verb "go" itself. 

I hope this helps! Here are some exercise: 
Choose the correct answer based on question.
1. When did he do it? 
 a) 他(是)昨天做的。
Tā (shì) zuótiān zuò de  ("zuò“ means "do"

 b) 他昨天做了。
Tā zuótiān zuò le

2. How did he do it?
a) 我教他了。
Wǒ jiāo tā le     ("jiāo" means "teach")

b) (是)我教他的。
(Shì) Wǒ jiāo tā de

3. Did he do it?
 a) 他昨天做的。Tā zuótiān zuò de
 b) 他昨天做了。Tā zuótiān zuò le

4. Who did it yesterday?
a) (是)他昨天做的。(Shì) tā zuótiān zuò de
 b) 他昨天做了。Tā zuótiān zuò le