[Grammar] What’s The Difference Between “As”, “Since” & “Because”?

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Look at the sentence above, can I change “because” to “as” or “since”? Well, I’m sure you will find out after learning the difference between them together with me!

“As”, “because” and “since” can be used as conjunctions to give the reason for an action or a situation.


When we use because, we are focusing on the reason. The reason is the most important part.

She spoke quietly because she didn’t want to bother others.

We often use because-clause at the beginning of a sentence, especially when we want to give extra focus to the reason.

Because breathing is something we do automatically, we rarely think about it.

We can use a because-clause on its own without the main clause in speaking or informal writing.

-Why did you stay up late last night?
Because I have to finish my work.

  • Warning:

We can’t use because-clause on its own in formal writing.

The journey was quite quick because the road was clear.(√)

The journey was quite quick. Because the road was clear.(×)


As, Since

As and since are used when the reason is already well known and is therefore usually less important.

  • He decided to go to the conference in Barcelona as he was in Spain anyway.

→ The speaker wants to focus on the fact that “he decided to…”

  • They’re rather expensive, since they’re quite hard to find.

→ The speaker wants to focus on the fact that they’re expensive.

Did you notice? We usually put a comma( , ) before since.

Just like because-clause, we can also use as and since clauses at the beginning of a sentence. Still, put a comma( , ) after the clause.

Since her husband hated holidays so much, she decided to go on her own.

As everyone already knows each other, there’s no need for introductions.


We use because, not as or since, in questions where the speaker proposes a reason:

Are you feeling unwell because you ate too much?
As or since can’t be used.


Okay, did you get the answer to the question at the beginning?

→ Why do you use U-Dictionary? Because I want to learn English!

Apparently, I am asking you for a reason and you’re answering me to give me the reason. All we’re focusing on is the reason, so “because” is the best one.


Are you upset ______ they mistook your meaning?

A. because            B. since              C. as

If you have any questions, leave a comment!

See you!

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