究竟 vs 毕竟jiūjìng vs bìjìng

Distinguishing Adverbs 究竟 (jiūjìng - after all in questions) and 毕竟 (bìjìng - after all in statements)

Meaning: 究竟: on earth / after all (in questions); 毕竟: after all (stating a reason)

Pattern

Although both 究竟 and 毕竟 can translate to "after all", their grammatical contexts are completely different: (1) 究竟 is used in QUESTIONS (or clauses containing an embedded question) to press for a clear answer, equivalent to a more formal 到底 ("on earth / after all", e.g., 你究竟为什么不告诉我？).
(2) 毕竟 is used in DECLARATIVE statements to point out an underlying fact that explains or excuses something ("after all / when all is said and done", e.g., 他毕竟是新来的，做错了一些事情可以理解).
Never use 究竟 in a plain declarative statement, and never use 毕竟 to press a question.

1
你究竟为什么不告诉我？
Nǐ jiūjìng wèishénme bù gàosu wǒ?
Why on earth won't you tell me?
2
他毕竟是新来的，做错了一些事情可以理解。
Tā bìjìng shì xīn lái de, zuò cuò le yīxiē shìqing kěyǐ lǐjiě.
After all, he is a newcomer, so it is understandable that he made a few mistakes.
3
我们究竟要等到什么时候？
Wǒmen jiūjìng yào děng dào shénme shíhou?
Until when on earth do we have to wait?

•究竟 is used only in questions (like a formal 到底), while 毕竟 is used only in declarative clauses stating a reason.

⚠️ Common Mistakes:

•Using 究竟 in a declarative justification where 毕竟 is required (*他究竟是个孩子 instead of 他毕竟是个孩子).

•Using 毕竟 in an information-seeking question where 究竟/到底 is required (*你毕竟想做什么？).

Combine Vocabulary, Grammar, Reading Practice, Listening, Hanzi Writing, and Mock Exams at HSK 5 to master all skills together.