Vietnamese classifiers can seem nuanced compared to other Asian languages. The following will summarize the ways they must and can be used within the language. Unless otherwise stated, these rules also apply to measure words, as these usually behave as classifiers do. #### Counting & Determiners Firstly, it should be noted that there are three types of nouns in regards to classifiers, and they are grouped based on their behaviour when being counted or used with a determiner, as well as with post-nominal relative clauses and possessive modifiers - Obligatory-classifier nouns - Optional-classifier nouns - Forbidden-classifier nouns The forbidden classifier noun group includes self-classifying nouns, which will be explained below. Simpson & Ngo (2018, Journal of East Asian Linguistics) call this group the Non-classified noun group, but I'm not a fan of that term since it includes the self classifying nouns too; hence my term of forbidden, simply implying you cannot add a classifier to the noun. ### Obligatory-classifier nouns In this group, when counting or using a determiner, a classifier is mandatory. Examples of this are: 1. Hai con mèo - Two cats 2. Một quyển sách - One book 3. Cái bàn đó 4. Chiếc xe này This also includes when using các and những Although there isn't a list anywhere you'll find of which nouns fall within this category, most concrete nouns representing physical objects will be in this category: animals, furniture, vehicles, etc. ### Optional-classifier nouns This group is made up of nouns that can be counted and determined with or without a classifier. Examples of this are: phòng, làng, nhà máy These are all correct: 1. Một phòng 2. Một căn phòng 3. Thiên thạch này 4. Khối thiên thạch này ### Forbidden-classifier nouns In this category, we have self classifying nouns, such as time units, money units, measurement units, and geographical units, since they inherently classify something already. These are words such as giây (second), phút (minute), giờ (hour), ngày (day), tuần (week), tháng (month), năm (year), tỉnh (province), nước (country) Additionally, words that belong to this group include abstract nouns like màu (color) and tiếng (sound), as well as Sino-Vietnamese compounds, like vương quốc (kingdom), quan điểm (viewpoint) Thiên thạch is an exception to this rule despite being a Sino-Vietnamese compound from 天石, because it is also a physical object; as a result, it takes the middle ground and becomes an optional-classifier noun. There is also the other Sino-Vietnamese word, vẫn thạch from 陨石. You will notice this pattern with other concrete SV nouns ### Environments where classifiers are not needed Outside of counting and using determiners, there are other situations when a classifier may or may not be needed. - Mass nouns - Generic references For example, one can say "tôi muốn mua sách" to mean "i want to buy books". Because we're neither counting nor showing definiteness, we do not need a classifier. ### Animate Nouns and Definiteness Animate nouns are very likely to be used with a classifier when they are definite. Bisang & Quang (2020) found that 92% of animate nouns when definite occurred with a classifier, while 27% of definite inanimate nouns occurred with a classifier. Inanimate nouns can often be initially referenced with a classifier and then drop it for the rest of the conversation as long as the intended meaning is still clear ### Double Classifier Since a classifier does not indicate definiteness on its own in Vietnamese, it's possible to see a double classifier construction that forces a definite interpretation of a phrase. For example, one might see: Hai cái con chó - The two dogs This forced definiteness can occur with all types of nouns mentioned above. It should be noted that research on this topic believes that this usage of cái is not technically as a classifier but as focus marker. ### Sources Classifier syntax in Vietnamese https://link.springer.com/article/10.1007/s10831-018-9181-5 DECOMPOSING DEFINITENESS IN VIETNAMESE https://evols.library.manoa.hawaii.edu/server/api/core/bitstreams/401d7d3d-3747-4763-8d15-f99a8c78f929/content (In)definiteness and Vietnamese classifiers https://www.semanticscholar.org/paper/(In)definiteness-and-Vietnamese-classifiers-Bisang-Quang/71c5dcbf43c9a15ed3a5cfdd121c75a12db23b02