As the title asks, why can't we use 2 conjunctions in a sentence? For example:
Because it is raining today, so I go out with umbrella.
It sounds correct in Chinese, but my teacher said that it's incorrect in English, without giving any reason.
Does anyone know the reason?
You can use many conjunctions in a sentence; but you have to use them the right way.
It's complicated, but here's a simplified explanation which handles the example you offer.
At clause level there are two sorts of conjunctions, which establish different relationships between the clauses they join.
a coordinating conjunction (Collins, so, 18-21 calls this a sentence connector) puts the two clauses it joins on the same ‘level’: each clause is syntactically independent.
Just for example, let’s suppose that there’s a network in which the members are obliged to pass on interesting news.
A so B
Jim told Agnes, so of course she told me.
In theory you can chain as many coordinating conjunctions as you want; the only limit to the number of clauses you can join this way is your hearer’s patience.
A so B so C so D so E ...
Harry told Louise, so she told Jim, so he told Agnes, so she told me, so I will tell Phyllis, so she will tell ...
This is not good written style, but it is very common in oral storytelling.
a subordinating conjunction puts the clause it introduces at a ‘lower level’ than the clause it is joined to. That is, the clause introduced by a subordinating conjunction is not independent: it plays a distinct role within the other clause.
A
because B
Agnes told me because Jim told her.
because Jim told her explains why Agnes told me.
Again, there is no theoretical limit on how many subordinations you may chain A because B because C because D ...
Agnes told me because Jim told her because Louise told him because Harry told her, because ...
Each clause explains the clause ‘above’ it.
Now: you are free to combine coordinating and subordinating clauses to express complex relationships, as long as you keep the relationships straight.
A so C
because B
Jim told Agnes because Louise told him, so Agnes told me.
But: what you cannot do is put two clauses in two different relationships to each other; and that is what your example does:
∗ Because it is raining today, so I go out with my umbrella.
A so B
because A
When you use both a subordinating and a coordinating conjunction, A shows up twice in the diagram. The meaning is clear, but syntactically A is assigned two conflicting roles, which is a no-no.
ADDED:
Just by the way: your construction was acceptable in older English, down to about the middle of the 17th century; but it disappeared in the ‘rationalization’ of formal discourse which occurred after the Restoration.
Note, by the way, that although because is always a subordinating conjunction, so plays different roles in different contexts. In the examples above, it is a coordinating conjunction; in other cases it may act as a subordinating conjunction:
Because it is raining today I’ll take my umbrella so I don’t get wet.
English, as I’m sure you’re aware, is full of traps like this.
CocoPop's answer was pretty good, but for a more formal answer:
A conjunction joins two sentences. In Chinese, from what I understand, the conjunction used here has two parts, but is one conjunction - the two parts must be used together.
The English conjunctions "because" and "so" are not two parts of one thing; each one is its own conjunction. SO when you use them together, you are doing the "job" of a conjunction twice, so it doesn't make sense.
Edit: As FumbleFingers points out in his comment, it is strictly speaking possible to use two conjunctions in one sentence; the problem is using them in one join.
At first glance, it seems to throw off the cause-and-effect balance of the sentence by introducing a redundancy that is difficult for the (native) listener to parse. Also, it makes it hard to justify the otherwise elegant "tent" contour of a true cause and effect statement:
/because it's raining/ \I'll take the umbrella\
-or-
/it's raining today/ \so I'll take the umbrella\
With two conjunctions, they're just flat statements with no coherence:
-because it's raining today- ... -so I'll take the umbrella-
Not a very scientific explanation, just my personal impression.
"Because it is raining today" implies that you are about to explain what will or did happen. Adding "so" is redundant. You could also say "It is raining today so I will go out with an umbrella."
Also, note that you need to change the tense on the second part to "I will" or "I went".
Finally, while technically correct, most English speakers would not say "go out with an umbrella". Go out with usually implies a romantic date. They would say, instead:
Because it is raining, I will take an umbrella.
It was raining, so I took an umbrella.
Good luck learning English!
To the student:
I'm sorry that your English teacher did not answer your question. I can easily understand your sentence, but I don't know how long you have been speaking, reading and writing English. Seems like you're doing pretty good with subjects, nouns and verbs.
Your sentence is a compound sentence. They use conjunctions and some make better sense than others (that means they don't sound goofy).
There are plenty of tenses, so here are the three basics. The past tense (what you "did" last week). The present tense (what you "do" right now), and the future tense (what you "will do" next week). The verbix.com web site has every verb in the English language. You will see the past tense, the present tense and the future tense (ignore all those other "tenses" until you are ready).
Your sentence (or part of it): I go out with umbrella. Yes...but "goofy." I "go out with" girls, or I "go out with" boys, or I "go out with" friends. BUT! I "take" an umbrella.
AND TO MAKE YOUR SENTENCE NOT SO GOOFY... Because it is raining, I will take an umbrella.
English "takes" time to learn. Hear (and see) how goofy it sounds if I wrote, "I go out with time."
So now you will only go out with girls, or boys, or friends AND YOU WLL NEVER GO OUT WITH UMBRELLA! Because you can not have fun with umbrellas, unless you are a goofy circus clown.
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The argument about beginning a sentence with a conjunction reminds me of a joke....
The upper-crust ladies from Hyannis Port Maine were in their seats and ready to go, looking forward to the beautiful springtime ride through historic Savannah Georgia. Their tour guide, a drop-dead gorgeous blonde, came aboard the bus and greeted them with a warm welcome, "And where are all y'all from?"
Every passenger went stone-cold quite, gave her a haughty snuff and looked away. Faces held that look of contempt until one sitting on the front seat curled her forefinger, motioning the Southern Belle to come closer. She whispered in a condescending tone, "We don't like to speak with people who begin their sentences with conjunctions, and end them with prepositions."
Blondie didn't miss a beat, cranked up the intercom and said with a big smile, "I do declare! All y'all queen bitches come from Hyannis Port Maine?!"
