Cambridge University:

When a clause follows these (subordinating) conjunctions , it becomes a subordinate clause, which needs a main clause to make a complete sentence. Link

Let's take a look at this example:

We went home early because we were tired.

Here, 'because we were tired' described as a incomplete thought and sentence due to mentioned grammar rules because it has followed a subordinating conjunction.

Well, in general, if someone in a conversation suddenly says, "because we were tired" It is an incomplete thought and sentence indeed.

But what if conversation goes like this:

A: We went home early. B: [I know] Because you were tired.

Here it isn't an incomplete thought even though the sentence has started with 'because' which we call it a subordinating conjunction.

Contradiction begins here. The clause 'you were tired' follows a subordinating conjunction but it doesn't need a main clause to make a complete sentence. It's already a complete sentence but with a subordinating conjunction.

  • 1
    When a clause is introduced by a subordinator, the whole sequence including the subordinator is a subordinate clause. In, for example, "I know [that Ed is a good teacher]" it is the whole bracketed sequence that is a subordinate clause.
    – BillJ
    Mar 28 at 8:13

2 Answers 2


"You were tired." is a complete sentence.

"...because you were tired." is not a complete sentence. It is the presence of the conjunction that makes it need a clause to be subordinate to.

There isn't any contradiction. Yes, in speech you can say "Because you were tired.", where both parties understand what was omitted, and that can make sense. But, people don't always speak in complete sentences.

  • therefore, you mean if we find a clause that follows a subordinating conjunction but it's understandable and complete, there is always an omitted part? Mar 28 at 6:37
  • I think so, unless you have an example to the contrary? Mar 28 at 6:51
  • 1
    That's the point, and It's completely logical; I didn't know main clauses can be omitted as well. Mar 28 at 7:04
  • 1
    A subordinate clause is an embedded clause that is dependent on some other element in the sentence. Modern grammar defines "because" as a preposition. "You were tired" is a clause that is dependent on the prep "because", and it thus qualifies as a subordinate clause.
    – BillJ
    Mar 28 at 8:00

A string of words may be a "complete thought" in the sense that it conveys understandable information. That is not the same as being a grammatically correct sentence.

Sure, if someone asked, "Why did you stop?" and you replied, "Because I was tired", we all understood what was meant. That does not make your response a complete, grammatically correct sentence.

Just like, if someone asked, "Where is my fork?" and you replied, "On the table", we all understand the meaning, but that does not make "On the table" a complete, grammatically correct sentence.

I could give many examples of strings of words that convey useful information but are not complete sentences. In casual conversation, we do this all the time. If someone asks, "Who was that man I saw you with yesterday at the restaurant?", most people would reply with something like, "My friend Bob". Very few would reply with a complete sentence, like, "The man that you saw me with yesterday at the restaurant was my friend Bob."

  • So can we conclude that every clause with a subordinating conjunction at the beginning that has a complete thought has an omitted part? Like: [I stopped] Because I was tired. Is the main clause [I stopped] omitted here? Mar 28 at 6:50
  • 1
    @KavehBehnia A subordinate clause is not defined semantically but grammatically. It's an embedded clause that is dependent on some other element in the sentence.
    – BillJ
    Mar 28 at 7:47
  • I still remember teachers who expected us to answer in complete sentences. So if they asked "What is the sum of two and three?" you were supposed to respond something like "Two plus three is five." But this kind of repetition of the question is redundant and not common in casual speech (when done, it's usually for some rhetoric purpose, like emphasis).
    – Barmar
    Mar 28 at 15:06
  • Just saying "Because I was tired" is nonsensical. It must be providing a reason for something. For instance "You've stopped going to the gym?" "Because I was tired." Here you could replace the response with the complete sentence "I've stopped going to the gym because I was tired."
    – Stuart F
    Mar 28 at 16:33
  • 1
    @barmar Yes! When I was in school teachers regularly insisted that answers to questions on tests must be complete sentences. My chemistry teacher once asked why we repeated the question in our answers on his tests, and several students said that was required by other teachers. He said, "If I ask what compound is produced when you mix two chemicals, just tell me the name of the compound. You don't have to say, 'Yes indeed, when you mix A and B there is a chemical reaction'."
    – Jay
    Mar 30 at 6:55

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .