那时

You usually place 那时 at the very beginning of your sentence or right after the subject. Think of it as a time-stamp for your thought. If you are telling a story about your college days, you might start with 那时，我每天都喝五杯咖啡 (At that time, I drank five cups of coffee every day). It acts as a frame for the rest of your sentence. You don't need fancy grammar to make it work. Just drop it in before the action happens. It works perfectly with words like 还 (still) or 已经 (already) to show what was happening in that moment. It is like setting the scene in a movie before the actors start speaking. Just don't use it for the future; it only looks in the rearview mirror.

You will hear this a lot in heart-to-heart conversations or late-night chats. Imagine you are at a café with an old friend. You might say, 那时我们都很年轻 (We were so young back then). Or maybe you are watching a period drama on Netflix. The narrator might say, 那时，还没有互联网 (At that time, the internet didn't exist yet). It is also common in song lyrics about lost love. In a WhatsApp message, you might send a photo of an old Nokia phone and type, 那时这就是最酷的东西 (This was the coolest thing at that time). It is the perfect phrase for any "glow-up" post where you show a clumsy old photo next to your current stylish self. Even in job interviews, you can use it to describe a past role: 那时，我负责市场部 (At that time, I was in charge of the marketing department).

Use this phrase when you have already established a specific time in the conversation. If you just said, "I lived in London in 2010," your next sentence should start with 那时. It keeps the flow smooth. It is great for storytelling, writing in a journal, or explaining the history of a company. It is also the go-to phrase for reminiscing about childhood. If you want to sound a bit more thoughtful and less casual than 那时候, this is your best bet. It is neutral enough for a business meeting but warm enough for a date. It is especially useful when you want to emphasize that a certain condition was true back then, even if it isn't true anymore. It is the king of nostalgic comparisons.

Don't use 那时 to talk about the future. If you mean "at that time tomorrow," you need a different phrase like 到时候. 那时 is strictly for the past. Also, don't use it for very short, immediate moments that just happened five seconds ago. For that, 刚才 (just now) is much better. If you are in the middle of a fast-paced action scene, 那时 might feel a bit too slow and reflective. It is a slow-motion phrase, not a high-speed one. Also, avoid using it if you haven't already mentioned which "time" you are talking about. If you just walk up to a stranger and say 那时很冷, they will wonder, "Which time?!" You have to set the stage first.

Learners often try to use 那时 for future appointments, but it just sounds weird to a native speaker. Another common slip is using it instead of 当时.

While they both mean "at that time," 当时 is for the immediate reaction to an event. 那时 is for a general period or era. Using 那时 for a sudden accident feels like you are looking at a car crash through a telescope instead of being right there. Keep 那时 for the "big picture" memories and 当时 for the "right then and there" moments.

The most common cousin is 那时候 (nà shí hou). It means the exact same thing but feels more casual. You'll hear 那时候 90% of the time in daily speech. If you want to sound a bit more poetic or literary, you can use 彼时 (bǐ shí), which is very formal and often found in novels. Then there is 当年 (dāng nián), which specifically refers to "those years" or a certain era, like "back in the day." If you are talking about a specific day, use 那天. If you want to say "at the same time," use 同时也. Each one has a slightly different flavor, like different filters on a camera. 那时 is the standard, reliable filter that looks good on almost any past memory.

You can add a few words to spice it up. 就在那时 (jiù zài nà shí) means "exactly at that time," which adds a bit of drama. It is like saying "right then!" in a story. You might also hear 到那时为止 (dào nà shí wéi zhǐ), which means "up until that time." This is great for explaining how long a situation lasted. If you are comparing two different periods, you might say 比起那时 (compared to that time). In many Southern Chinese dialects, people might lean more heavily on the 那时候 version, adding the 候 to make it sound softer. In writing, you'll see it paired with 由于 (due to) to explain why things were different back then.

Is 那时 formal? It is neutral! You can use it with your boss or your best friend. Is it different from 那时候? Only slightly; 那时候 is more common in spoken Mandarin, while 那时 is a bit more concise and common in writing. Can I use it to start a story? Yes, as long as the listener knows which era you are talking about. Does it imply sadness? Not necessarily, but it often carries a bit of nostalgia because you are looking back at the past. Can I use it for a specific hour? No, use 两点 (two o'clock) or 那个时间 for specific clock times. 那时 is for moments in history or life chapters.