Hi.
I don't know what happened that I fell in love with the piano.
What type of clause is the underlined part?
It's a content clause.
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I guess it can be a noun clause as an object for the verb 'know'. We should wait for native English to reply.
After some thought, I think it's an adverbial clause modifying 'happened'.
Hi Persian Learner,
Where did you find this sentence?
Could you please give me a source?
Persian LearnerI don't know what happened that I fell in love with the piano.
Formally, this sentence is not entirely correct English, in my opinion.
I don't know what happened that I fell in love with the piano.
The underlined content clause is a result adjunct in clause structure. It functions as adjunct to the preceding subordinate interrogative clause "what happened".
The meaning of the sentence can be glossed as "I don't know the answer to the question 'What happened with the result that I fell in love with th