Learners are often confused because là does not work exactly like the English verb “to be.” In Vietnamese, là is used only to link the subject with a noun or noun phrase. It is not used before adjectives. This is very different from English, where “to be” appears before both nouns and adjectives.
So Vietnamese sentences like “Tôi là bác sĩ” (I am a doctor) use là, but “I am tired” becomes “Tôi mệt”—no là needed.
Understanding this difference helps learners avoid one of the most common mistakes: saying “Tôi là mệt”, which is incorrect.
“Tôi là giáo viên.” → I am a teacher. (Correct: noun phrase → use là)
“Anh ấy mệt.” → He is tired. (Adjective → no là)
“Đây là nhà của tôi.” → This is my house.
“Trời nóng quá!” → It’s so hot! (Adjective → no là)
Use là before nouns, roles, jobs, names, definitions.
Do NOT use là before adjectives.