With 是…的 , we can emphasize an important piece of information in a sentence.
In English, it’s similar to emphasizing things by inverting the word order or using intonation.
For example, let’s compare:
“Yesterday I bought an apartment” is an ordinary narrative sentence.
However if we want to emphasize the word “apartment” we may say:
“I bought an apartment yesterday!”
So this is how the 是…的 construction works.
We may use this construction to emphasize anything: time, place, purpose, person, mode of action, etc. There can be just one word or a whole phrase between 是 and 的.
Who told you?
shì shéi gàosu nǐ de
I was born in Shanghai
wǒ shì zài shànghǎi chūshēng de
I came by train
wǒ shì zuò huǒchē lái de
We don’t use the construction 是…的 in the future tense.
We also use 是…的 to emphasize a person's opinion or attitude:
He did want to come
tā shì yuànyì lái de
It must be done
zhèyàng zuò shì yīnggāi de
Sometimes we may omit 是 and use only 的.
A friend told me this
zhè jiàn shì yí ge péngyou gàosu wǒ de
How to make the negation
To construct a negative sentence we should use the negative particle 不 before 是.
The negation does not refer to the whole sentence, but only to the part that is emphasized by the construction.
We cannot omit 是 in a negative sentence, therefore we must use the full structure 是…的.
They didn't meet last year
tāmen bú shì qùnián rènshí de
We're not perfect
wŏmen bú shì wánmĕi de
How to ask a question
We can ask 3 types of questions with this structure:
1) using the question particle 吗 :
Are you from Peking University?
nĭ shì bĕijīng dàxué de ma
2) reduplicating 是 with the negative particle — 是不是: