Learn Hardcore Chinese: nǐ rènshi tā duōjiǔ le?

Sentence-final 了 marks a current, changed state or “up-to-now” relevance. In 你认识她多久了？, it anchors the duration to the present, like English “How long have you known her?” Without it, the question can sound less clearly “up to now.”

Can I drop 了 and just say 你认识她多久?

You will hear this in casual speech, but 你认识她多久了？ is the standard way to ask “How long have you known her (up to now)?” Dropping 了 can sound less natural or less clearly tied to the present.

Could I say 你多久认识她了?

No. 多久 doesn’t go before 认识 here. Use 你认识她多久了？, 你们认识多久了？, or 你和她认识多久了？ instead.

Why use 认识 and not 知道 or 了解? What about 见过?

认识 (rènshi): to be acquainted with a person; to have met and know who they are.
知道 (zhīdào): to know a fact. Not used for being acquainted with a person.
了解 (liǎojiě): to understand someone/something in depth.
见过 (jiàn guo): have seen/met someone at least once, but not necessarily “know” them.
So 你认识她多久了？ asks about your acquaintance, not facts about her.

How do I answer naturally?

我认识她三年了。 (I’ve known her for three years.)
有三年了。 or 我认识她有三年了。 (as much as three years)
差不多十年了。 / 快五年了。 (about ten years / almost five years)
If it’s short: 我认识她没多久。 or 我认识她不久。

What’s the difference between 多久 and 多长时间?

Both can mean “how long (in time).” 多久 is shorter and very common; 多长时间 is a bit more explicit or formal. Don’t use 多长 alone for time; say 多长时间.

What does 有 do in 你认识她有多久了 or 我认识她有三年了?

有 before a duration often adds a sense of “as much as/at least,” and is common in speech. It doesn’t change the basic meaning: 我认识她三年了 ≈ 我认识她有三年了.

How is 认识 pronounced? Is it rènshi or rènshí?

In everyday speech, 认识 is commonly pronounced rènshi (neutral tone on 识). You may also hear rènshí, but rènshi is very standard in the Mainland.

Is 她 (tā) pronounced the same as 他/它? How do people tell?

Yes, all are pronounced tā. In speech, context tells you which one is meant. In writing, the characters differ. If needed, people clarify with 女的她 (the female “ta”).

How do I say I don’t know her, or I haven’t known her long?

“I don’t know her”: 我不认识她。
“I haven’t known her long”: 我认识她没多久。 / 我认识她不久。
Avoid 我没认识她 for this meaning; it’s unidiomatic.

Why not say 你认识了她多久?

Placing 了 right after 认识 makes it the perfective 了 (completed action), which clashes with asking a duration like 多久 for a continuing state. Use the sentence-final 了: 你认识她多久了？

Difference between 你认识她多久了 and 你是什么时候认识她的?

你认识她多久了？ asks for the length of time up to now (duration).
你是什么时候认识她的？ asks for the specific time you first met (point in time).

Can I say 你们认识多久了 or 你和她认识多久了?

Yes. 你们认识多久了？ and 你和她认识多久了？ are both natural and avoid repeating 你…她.

When do we use the “two-了” duration pattern?

For ongoing activities: V + 了 + duration + 了, e.g., 我学中文学了三年了。 or 我等了你一个小时了。 With the stative/acquaintance verb 认识, we normally say 我认识她十年了 (no first 了).

Is there a polite version with 您?

Yes: 您认识她多久了？ Using 您 adds politeness toward the addressee.

How do I ask about time needed (future/process) rather than time elapsed?

Use 要/需要 + 多久:

到车站需要多久？ (How long does it take to get to the station?)
我们还要等她多久？ (How much longer do we have to wait for her?)