classifiers are required before a nouns when referring to a specific noun such as "the cat", "this dog", or "those birds".
classifiers are also required when stating the number of a noun such as "a dog", "two trees", or "a few birds".
classifiers are not used when talking referring to the noun generally as in "I like dogs" or "Trees are good for the environment".
cái
inanimate objects - ????
con
animals - dogs, cats, birds, etc.
cây
stick-like objects - trees, plants, guns, canes, etc.
chiếc
objects worn or moved by people - shirt, shoes, car, chair, etc.
quả/trái
globular objects - Earth, fruits, etc.
quyển/cuốn
book-like objects - books, journals, etc.
tờ
thin objects made of paper - newspaper, paper, calendar
việc
an event or an ongoing process - ???
người
people - man, woman, Vietnamese person, etc.
bài
compositions - songs, drawings, poems, essays, etc.
tòa
buildings of authority - courts, halls, etc.