A lot of learners make mistakes with the character 是
This character often means ‘to be, am, is, are’ or ‘it is so’.
BUT it doesn’t work exactly the same as the verb ‘to be’ in English or other languages.
When using an adjective to describe something, or talking about a state of being, like being cold/thin, you don’t use 是 on its own
我是饿 should be
我饿了 wǒ è le or
我很饿 wǒ hěn è
I am hungry
他是很胖 should be 他很胖 Tā hěn pàng
He is very fat
这件毛衣是黄色 should be
这件毛衣是黄色的
Zhè jiàn máoyī shì huángsè de
This sweater is yellow
But you do normally use 是 when talking about somebody’s status or job.
我是英国人
Wǒ shì yīngguó rén
I am British
他是医生
Tā shì yīshēng
He is a doctor
她是学生
Tā shì xuéshēng
She is a student
她是单生的
tā shì dānshēng de
She is single
(but not 她是结婚, she is married would be 她结婚了 tā jiéhūn le）
你是对。
You’re right.
This should be 你对了 Nǐ duì le
or 你说得对 nǐ shuō dé duì。
But sometimes we may add 是 to a sentence and stress it to make a point stronger.
你是对的。
Nǐ shì duì de.
You are right.
(I maybe didn’t think you were before).
And here’s another example:
你很聪明
Nǐ hěn cōngmíng
You are very clever/smart.
Normally we wouldn’t say 你是很聪明, unless we particularly want to emphasise this fact, in which case we would say:
你是很聪明。
Nǐ shì hěn cōngmíng
You are very smart.
(Maybe you don’t believe it yourself or other people don’t say so, but you are)
Some more examples
我一直在看书
wǒ yīzhí zài kànshū
I have been reading a book (all this time)
我会永远爱你
wǒ huì yǒngyuǎn ài nǐ
I will always love you.
我是上周到的
wǒ shì shàng zhōu dào de
I arrived last week.