是 + noun
Reach for 是 when you want to equate two nouns — 'A is B,' where B is a noun (or noun phrase). It's the equivalence verb, used for identification, categorization, and definitions. Critically, 是 only links nouns to nouns. To link a subject to an adjective ('I am tired'), you don't use 是 at all — you use the adjective on its own (我累了). Mixing this up is the single most common beginner mistake.
Structure
[SUBJECT] 是 [NOUN]
shì + [NOUN]
How to Think About It
是 is an equals sign, not a state verb. It joins two nouns and says 'these refer to the same thing or category.' That's why adjectives don't take 是 — an adjective isn't a noun, so there's nothing to equate. If you ever feel tempted to write 是 + adjective, ask 'is the right side a noun?' If no, delete 是. The only exception is 是 + adjective + 的, which turns the adjective into a noun phrase.
Examples
他是我的老师。
Tā shì wǒ de lǎoshī.
He is my teacher.
这是一个问题。
Zhè shì yí ge wèntí.
This is a problem.
义乌是一个城市。
Yìwū shì yí ge chéngshì.
Yiwu is a city.
Common Mistake
Beginners insert 是 in front of adjectives by reflex from English 'is.' But 我是累 is ungrammatical; the adjective stands alone (with 很 as a default filler).
我是高。
我很高。
Don't Confuse With
[SUBJECT] + ADJECTIVE
For 'I am tall,' drop 是 and use 我很高. 是 only links nouns; adjectives work on their own as the predicate.
在 + [PLACE]
Use 在 for location ('A is at / in B'), not 是. 他在北京 = he is in Beijing; 他是北京人 = he is a Beijinger.
[SUBJECT] 是 [ADJECTIVE] 的
是 + adjective + 的 is allowed because 的 nominalizes the adjective. 这本书是红的 = 'this book is the red one.'
Practice
Fill in the blank: 他 ___ 我的老师。 (he is my teacher)
Show answer
是
Fill in the blank: 这是 ___ 个问题。 (this is a problem)
Show answer
一
Arrange: 老师 / 我的 / 他 / 是 / 。
Show answer
他是我的老师。
Translate to Chinese: This is a problem.
Show answer
这是一个问题。
Write a sentence using 是 to identify yourself by your profession or nationality.
Show answer
我是一个学生。
Hear It in Real Episodes
This pattern appears in 1 Fluentide episode: