Nouns Have No Plural

In English, we change the noun itself to make it plural (book → books, child → children). In Vietnamese, nouns generally do not change form to show plurals.

A plain noun like sách (book) is number-neutral. Depending entirely on the context, it can mean "a book", "books", or "books in general".

When you need to be specific about quantity, you don't change the noun. Instead, you add words before it:

• Numbers: Use a number plus a classifier (e.g., hai quyển sách = two books). Note that some words do not need an additional classifier, such as time words (ngày, tháng), units of measurement, or words that already function as classifiers themselves, like người (person) (e.g., hai người = two people).
• Plural Markers: Use words like những (an indefinite plural or specific subset), các (a definite plural for all of a known set), vài / một vài / mấy (a few), or một số (some). Classifiers are generally required after the plural marker những for nouns that normally take them, including physical objects, animals, humans, and abstract concepts (e.g., những đứa trẻ = some children, những cuốn sách = some books, những niềm vui = some joys). However, classifiers are frequently dropped after các in general, formal, or collective contexts, even for nouns that normally take them (e.g., các nước = the countries, các trường = the schools). Nouns that do not take classifiers—such as many abstract words (e.g., những ý nghĩ = some thoughts, các vấn đề = the problems) or Sino-Vietnamese compounds (e.g., các sinh viên = the students)—simply attach directly to the plural marker.
• 'All' and 'Every': To express "all", you can place tất cả before a plural marker (e.g., tất cả các sinh viên = all the students). However, tất cả can also attach directly to the noun without a plural marker, especially for Sino-Vietnamese words or general categories (e.g., tất cả sinh viên = all students). To express "every", use mọi before the noun. Note that in everyday speech, mọi generally requires a classifier if the noun normally takes one (e.g., mọi quyển sách = every book, mọi con chó = every dog). Do not confuse mọi with mỗi (each) or từng (each individually / one by one). While mọi looks at the group as a whole, mỗi focuses on each individual item (e.g., mỗi ngày = each day), and từng emphasizes going through them one at a time (e.g., từng người một = each person one by one).

Because plurals are obligatory in English, English speakers tend to overuse words like những and các. In Vietnamese, native speakers frequently drop plural markers entirely if the context, or a quantity word like nhiều (many), already makes it obvious that there are multiple items.

Additionally, you can use các before kinship terms and some pronouns to make them plural (e.g., bạn = you/friend → các bạn = you all/friends; anh ấy = he → các anh ấy = they). While các anh ấy is correct for a specific group of men, the standard, neutral word for 'they' is simply họ. Using các with kinship terms is also the standard way to address a group directly (e.g., Chào các anh chị = Hello everyone). The word chúng is used to pluralize certain pronouns, such as tôi (I) → chúng tôi (we, excluding the listener), ta (I/we) → chúng ta (we, including the listener), and mày (you, informal) → chúng mày (you all). Furthermore, combining chúng with a kinship term forms an exclusive 'we' based on your relationship to the listener (e.g., chúng em or chúng anh = we [excluding the listener]), whereas using các with a kinship term forms a plural 'you' (e.g., các anh = you all). In everyday spoken Vietnamese, bọn and tụi are also extremely common plural markers for groups of people and pronouns (e.g., bọn mình = we, tụi nó = they).

Finally, repeating a noun (reduplication) is a slightly poetic way to indicate 'every' or a plural totality (e.g., người người = everyone, nhà nhà = every house). However, this is not a productive grammar rule that you can apply to any noun. It is limited to a very small, fixed set of basic words (like người người, nhà nhà, ngày ngày, tháng tháng). You cannot reduplicate regular nouns like sách or mèo. Overall, because nouns do not change form, you will not have to memorize irregular plural forms.