是 (shì) is not exactly the same as “to be”
The closest equivalent of the English word “to be” in Chinese is 是 (shì). This is used to link nouns to other nouns. The structure is:
[noun] 是 [noun]
Let’s have a look at some examples:
我是学生。
Wǒ shì xuéshēng.
I am a student.
他是老师。
Tā shì lǎoshī.
He is a teacher.
她是医生。
Tā shì yīshēng.
She is a doctor.
这是书。
Zhè shì shū.
This is a book.
Notice how 是 is used to talk about one noun being another. You can’t use 是 to link adjectives to nouns, though, as in “this book is heavy”. To do that, you have to use 很 (hěn).
The basic structure for 很 (hěn) is the same as for 是, but 很 is used with adjectives. Have a look at some example sentences:
这本书很重。
Zhè běn shū hěn zhòng.
This book is heavy.
她很高。
Tā hěn gāo.
She is tall.
我们很高兴。
Wǒmen hěn gāoxìng.
We are happy.
Sometimes 很 is translated as “very”, but opinions vary on how accurate this is. We think it’s simply used to link adjectives to nouns, whilst others think it also intensifies the adjectives.
