ở

The word ở is one of the most common and important words in Vietnamese. It has several main functions:

1. As a Main Verb (To be located / To live / To stay)
When used as the main verb in a sentence, ở means that someone or something is located at a specific place, lives somewhere, or is staying somewhere temporarily (like a hotel: Tôi ở khách sạn). You do not need another 'to be' verb. Note that while ở can mean either a temporary stay or a permanent residence, the word sống specifically implies long-term living or residing (e.g., Tôi sống ở Hà Nội - I live in Hanoi).

• Pattern: [Subject] + ở + [Location]

2. As a Preposition (At / In / On)
When there is already an action verb in the sentence, ở acts like a preposition to show where that action is happening. Note that ở is generally for stationary locations or the final resting place of an object (like để ở trên bàn - put on the table). For destinations with verbs of motion, you usually use directional words like đến. However, if the motion happens entirely within a location, you use ở. Compare: Tôi chạy đến công viên (I run to the park - destination) vs. Tôi chạy ở công viên (I run in the park - action contained within the park).

• Pattern: [Subject] + [Action Verb] + ở + [Location]

3. Asking "Where" (ở đâu) and Pointing Locations
To ask where someone is or where an action happens, combine ở with the question word đâu (where).

• Bạn ở đâu? (Where are you? / Where do you live?)
• Bạn làm việc ở đâu? (Where do you work?)

To answer, you can use specific places or point to locations using đây (here), đó (there), or kia (over there). For example: Tôi ở đây (I am here) or Nó ở đó (It is there).

4. Indicating a State or Condition
Beyond physical location, ở can also describe a state of being or how someone lives and behaves. For example, ở dơ (to be messy/dirty) or ở trần (to be shirtless).

Important Nuances:
First, regarding time, ở is not used for specific clock times (where you would use lúc), nor is it used for days, months, or years (where you must use vào). However, it can be used for broader time periods, life stages, or specific points in time (e.g., ở thế kỷ 21 - in the 21st century, or ở độ tuổi 40 - at the age of 40).

Second, by itself, ở is a generic location marker. If you want to be specific about spatial relationships, you pair it with spatial words like trên / dưới / trong / ngoài using the pattern [ở] + [spatial word] + [noun]. Common pairings include: ở trong (inside / in), ở ngoài (outside), ở trên (on / above), ở dưới (under / below), ở trước (in front of), ở sau (behind), and ở giữa (in the middle of / between). For example, ở bàn means 'at the table', but to say 'on the table', you must say ở trên bàn. In casual spoken Vietnamese, ở is frequently dropped when paired with these spatial words (e.g., Tôi đang ở trong phòng often becomes Tôi đang trong phòng).

Because Vietnamese has no verb conjugation, ở never changes its form regardless of who is speaking or when the action happens.