This question already has an answer here:
The phrase "never knew who to trust" is from a fairly recent popular song.
It should be "never knew whom to trust".
My question is: how do you reach that change?
Is it because "whom to trust" functions as the object of the verb "knew"? If I recall correctly, in Latin, when you have an indirect question or an indirect statement, the relevant indirect phrase following the verb is in the nominative rather than the accusative. So in that language, it would actually be "who". Can anyone confirm my recollection?
Or is it also because in the phrase "whom to trust", "whom" is the object of the verb "trust"?
Either way, you reach the relevant change. I'd be grateful for your thoughts.
Note: this is not a duplicate of the linked questions. There are two elements here, first the accusative (not dative) object of the verb and second the indirect question with complement. That second element has not fully been answered.