We can agree that both
My brother felt sick.
He ate too many chocolates.
Are both independent clauses and that “because” “joins” them. So why is “because he ate too many chocolates” analysed as a clause and not “my brother felt sick because”?
Conjunctions and complementizers in English are typically analysed to attach in front of a clause, transforming an independent clause into a subordinate one, this is in reverse of, say, Japanese, where they tend to attach at the back of clauses — why is this analysis favored?
Firstly, the order can be reversed:
Because he ate too many chocolates, my brother felt sick.
This is already a strong argument that “because” attaches to “he ate too many chocolates” and the entire subordinate clause then joins with the independent clause.
Another is how that an inquiry in English can be answered simply with “Because he ate too many chocolates.”, this is also how sentences are typically broken up and feel natural to native speakers, if a sentence were spread out with a pause, this would feel unnatural:
He fell sick because
he ate too many chocolates.
“because” would almost always be moved over the pause, which is what feels more natural to English native speakers.
This is how conjunctions in English are generally analysed. “you and I” in English would similarly be broken down. That they attach to the front rather than the back can also be seen in such constructs as “either this or that” or “both you and I”.
Edit: After giving it some further thought, methinks English has two fundamentally different classes of conjunctions, one functioning as complementizers grammatically, and the other not. “and”, “or”, and “therefore” are grammatically fundamentally different from “because”, “since”, and “so that”.
Namely, sentences such as:
I, because I need to eat, sell my body for a living.
My dog, since he is hungry, is barking.
Are all possible, complementive clauses created by attaching the first group before a sentence can be inserted relatively freely inside of the matrix clause, as such one can far more easily argue that they are truly subordinate to said clause.
However with “or” or “therefore” it becomes more difficult:
*I, therefore I am, think.
*I, or took a bath, had something to eat.
Clearly “or”, “and”, and “therefore” do not create similar complementive subordinate clauses that can be inserted inside of their matrix clause, but only after it.
However, even with those the argument remains that “Or I had something to eat.” feels as a natural, complete utterance, whereas “I took a bath or.” feels as if it be wanting for a conclusion, an unfinished thought, therefore I would still argue that “or”, “therefore” and “and” attach to firstly to the second part of the conjunction, and the result of that then attaches behind the first independent clause to create a conjunction of two clauses.