Subordinating Conjunctions

Have you ever written a sentence like this in an essay?

I didn't finish my homework, I was playing games.

Your teacher circles it in red and scribbles "run-on sentence" or "comma splice." You stare at it and think, "But that's how I'd say it!" Your instinct is right that those ideas belong together. What you're missing is the little word that shows how they belong.

That's where subordinating conjunctions come in — words like because, although, when, if. They connect one idea to another and show the relationship: time, reason, contrast, condition. Once you're comfortable with them, your writing stops sounding like a list of simple sentences and starts flowing like proper, confident English.

Independent and dependent clauses

A clause is a group of words with a verb. Some clauses can stand alone as full sentences — these are independent clauses (I was late). Others feel "unfinished" and need another clause to make sense — those are dependent clauses.

• I was late. ✅ (independent — feels complete)
• Because I was late… ❌ (dependent — feels like something's missing)

That "something's missing" feeling is your clue. The word doing that job is usually a subordinating conjunction: it introduces a dependent clause and shows the relationship between that clause and a main clause. We'll focus on four common ones, plus a few relatives:

• because (also since, as) — gives a reason: We went inside because it was raining.
• although (also though, even though) — shows a contrast: I answered although I wasn't sure.
• when (also while, before, after, until) — shows time: We lined up when the bell rang.
• if (also unless, provided that) — shows a condition: You can go out if you finish your homework.

These are called adverbial clauses, because like adverbs they tell you more about the action in the main clause.

Watch out: don't write a dependent clause as if it were a complete sentence. Because it was raining. ❌ Instead: We went inside because it was raining. ✅

Clause order and commas

Here's the punctuation, which is the bit that matters for your writing.

When the dependent clause comes second, you usually don't need a comma:

• We went inside because it was raining.
• You can go out if you finish your homework.

When the dependent clause comes first, you usually do need a comma:

• Because it was raining, we went inside.
• If you finish your homework, you can go out.

That comma is a reader-friendly pause. It says: right, that's the end of the "extra information" — here comes the main point. A good test: read your sentence aloud. If you naturally pause between the two parts, you probably need a comma there.

Fixing the comma splice

A very common mistake is sticking two complete sentences together with just a comma and no joining word — a comma splice:

• I was tired, I went to bed. ❌

You can fix this three main ways:

1. Use a full stop [US: period]: I was tired. I went to bed.
2. Use a co-ordinating conjunction: I was tired, so I went to bed.
3. Use a subordinating conjunction to make one clause dependent: Because I was tired, I went to bed.

That last option is what we're practising here.

The tricky bits

Some conjunctions do more than one job, and you use context to tell which:

• Since can mean because or from that time: Since you're free, help with the posters (reason) vs I've been nervous since the results came out (time).
• While can mean during the time that or whereas/although: While I was waiting, I read a chapter (time) vs While maths is her strength, English takes more work (contrast).
• As can signal time, reason, or manner — so if precision matters in an exam, swap in because or when so the reader isn't left guessing.

Clause order changes emphasis, not meaning. Because I was ill, I stayed in puts the spotlight on the reason; I stayed in because I was ill puts it on what you did. Writers use this deliberately: When the whistle blew, the crowd roared has a dramatic build-up.

Don't confuse these with relative clauses. Subordinating conjunctions introduce adverbial clauses. Words like who, which, that, where introduce relative clauses, which describe a noun instead of giving a reason, time, or condition:

• The boy who was late missed the bus. (relative — tells us which boy)
• The boy missed the bus because he was late. (adverbial — tells us why)

For the full picture on relative clauses, see that article.

Watch out: a dependent clause standing alone is a sentence fragment — If you tell anyone. ❌ In an exam or formal essay these are usually marked wrong, though in fiction and dialogue they can create drama. The skill is knowing which register you're in.

Quick check

1. Underline the dependent clause and circle the subordinating conjunction: We stayed at school because it was raining heavily.

2. Add a subordinating conjunction: ___ it stopped snowing, we went outside to play.

3. Rewrite this comma splice using a subordinating conjunction: It was very noisy, I couldn't concentrate.

4. Add a comma if one is needed: If you see Mia tell her I called.

5. Is the bold clause adverbial or relative? The teacher smiled when she saw our marks.

Where next

• What Is Grammar? — foundational overview
• Coordinating & Correlative Conjunctions — joining equal ideas, not dependent ones
• Conjunctions of Time, Cause, and Contrast — a wider toolkit beyond our four
• Relative Pronouns (who/whom/which/that) — clauses that describe nouns, not actions
• Independent and dependent clauses — the full picture, in the Sentences pillar.