Feelings as nouns: nỗi buồn, niềm vui

Some feelings turn into nouns with a word in front: nỗi for feelings that hurt, niềm for feelings that lift you. Buồn (sad) gives nỗi buồn, sadness; nhớ (miss) gives nỗi nhớ, longing; lo (worry) gives nỗi lo, a worry. Vui (glad) gives niềm vui, joy; tin (believe) gives niềm tin, trust or faith; tự hào (proud) gives niềm tự hào, pride.

Use them where English needs a noun, as the subject or after là, có or mất: Nỗi lo lớn nhất của em là tiền nhà. My biggest worry is the rent. Con là niềm tự hào của ba mẹ. You're your parents' pride and joy. The feeling decides the word, so nỗi vui sounds wrong. Songs sometimes bend this, as in niềm đau (pain).

In conversation, Vietnamese usually keeps the plain word: Em buồn quá (I'm so sad), rather than a sentence about nỗi buồn. The nouns are at home in songs, stories, speeches and posts, and in a few everyday phrases such as niềm vui and nỗi nhớ nhà (homesickness).

Sự makes nouns from many verbs and adjectives, mostly in writing: sự giúp đỡ. Nỗi and niềm are only for feelings. Tới nỗi (so much that) is a different job.