Learn English – the function of but in the sentence

clausesconjunctionssubordinate-clauses

I don't know why but for some reason when I got on the train that
day it was unusually full, something I don't recall ever happening in
the past.

As for the above sentence, I have some questions:

  1. Is why a conjunction or adverb? My own understanding is that why is an adverb here which modifies the verb know, and but is the conjunction which connects two clauses. Is that true?

  2. As I read on Grammarly.com, when but is joining two independent clauses, we need to put a comma before it. Otherwise, leave the comma out. According to this rule, the two clauses are 'I don't know why' and 'for some reason when I got on the train that day it was unusually full, something I don't recall ever happening in the past.' But since there is no comma and the second clause doesn't express a complete thought, the second clause is a dependent clause or subordinate clause. Is that right?

  3. someone told me that the whole sentence is an object clause after why, but if the above clues are correct, then the sentence is not a object clause.

Best Answer

The general form "I don't know [question word], but" is a common idiomatic expression. The overall intent is to indicate some measure of surprise at an unexpected or unusual situation.

I don't know how, but the cat got on top of the roof and now she can't get down.

I don't know why, but the mayor thought it was a good idea to hold a press conference during a thunderstorm.

I don't know exactly who, but somebody ate all the chocolate cake I had been saving.

I don't know when, but some time recently the clocks were all reset.

And so on. I would memorize and practice it like any other idiomatic expression, as a complete phrase, since the individual words are not as important.

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