So, a teacher explained to me that 究竟 is a more formal way of saying 到底. However, I'm still curious if there are there any other usage differences between the two? Is 究竟 only used in examples that are relatively “夸张”
Chinese Language Stack Exchange is a question and answer site for students, teachers, and linguists wanting to discuss the finer points of the Chinese language. It only takes a minute to sign up.Sign up to join this community
When used as an intensive, they are synomymous. Both translated as "on earth," "exactly."
究竟, 穷尽. literally means "investigate to the end." It can also be used as a noun which means "outcome," "final truth."
究 谋划;研究;探求. Study, investigate. Originally means "exhaust," "limit." See http://xh.5156edu.com/html3/15922.html
竟,终了，完毕. End, finish. See http://www.zdic.net/z/20/js/7ADF.htm
到底, 直到尽头. Literally means to "the bottom," "to the end."
We must fight on until the end.
This is described in more detail in the textbook 标准教程HSK4下 on pages 132-133, which says:
Similarity: Both can be used as adverbs in interrogative sentences of sentences with an interrogative word to indicate inquiry and strengthen the interrogative mood. Both can only be put before the subject if the subject is an interrogative pronoun.
Differences: "到底" can be used as a verb, meaning "till the end", while "究竟" has no such usage.
It also describes 究竟 as follows:
... It is often used in written Chinese. If the subject of the sentence is an interrogative pronoun, "究竟" can only be put before it.
The Chinese Grammar Wiki further highlights how 究竟 is more formal than 到底:
When someone asks you "what on earth are you doing?," "究竟 (jiūjìng)" is used by the speaker to intensify the question. In this case, 究竟 is similar to 到底. ... Note that 究竟 is more formal than 到底.
Expressing "in the end" with "jiujing"
1 When used as adverbs
Both 到底 and 究竟 can be used as adverbs, and they are nearly the same when they are used to emphasize or to express strong emotion(normally negative ones). In this situation, the only difference is 究竟 is more formal than 到底. Here are a few examples.
When used as an adverb, 到底 can express the meaning of till the end, finally. 究竟 does not have this usage. But we use 最后 or 终于 more often. Some people use 到底 more often, so you can see this usage as a personal style.Here are a few example.
他们到底去了欧洲。They went to Europe finally.
你们到底还是不相信我。They did not trust me till the end.
我们公司到底把你们请来了。Our finally successfully invited you in the end.
2 other differences.
究竟 can be used as a noun, it means result, reason, things that happened. A few examples.
我们都想了解一下究竟。 All of us want to know what happened.
无论什么问题，他都会问个究竟。 Whatever the question is, he asks everything.