Yes, when you use it as an adverb. 1 到底 a actually, exactly 究竟是怎么回事？ b after all, finally 她究竟经验丰富，说的话很有道理。 for this meaning, 到底 and 究竟 are exchangable. 2 outcome, what are really happened? 大家都想知道个究竟。Everybody wants to know what actually happened. 我要问个究竟。I am going to question what realy happened.