Common Punctuation Problems

B1 · IntermediatePunctuation

Comma splices, run-ons, its/it's, and other punctuation traps — brought together in one place.

What you'll learn

  • A comma splice joins two full sentences with only a comma and no conjunction — add a conjunction or use a period instead
  • A run-on sentence joins two full sentences with no punctuation at all
  • 'its' (no apostrophe) is possessive; 'it's' (with apostrophe) means 'it is' or 'it has'
  • A plain plural (more than one thing) never takes an apostrophe
  • English doesn't normally add a comma before 'that' or 'because' introducing essential information, and rarely needs more than one exclamation mark

The most common punctuation traps

This lesson brings together the punctuation mistakes that come up most often across all the topics in this category — comma splices, run-on sentences, the its/it's confusion, apostrophes on plain plurals, and a few smaller habits worth breaking. If a mistake looks familiar from an earlier lesson, that's intentional: seeing them side by side helps make the patterns stick.

"It was raining, so I stayed inside. (correct)"
"It was raining, I stayed inside. (comma splice)"

Comma splices and run-on sentences

A comma splice joins two full sentences with only a comma, no conjunction: 'It was raining, I stayed inside.' A run-on sentence goes even further and joins them with no punctuation at all: 'It was raining I stayed inside.' Fix either by adding a conjunction after the comma, splitting into two sentences with a period, or using a semicolon if the two ideas are closely related.

"It was raining, so I stayed inside. (comma + conjunction)"
"It was raining. I stayed inside. (two sentences)"
"It was raining; I stayed inside. (semicolon)"

Apostrophe traps

'its' (no apostrophe) is the possessive form of 'it'; 'it's' (with apostrophe) is always a contraction of 'it is' or 'it has'. Separately, a plain plural — simply more than one of something — never takes an apostrophe: 'two cats', never 'two cat's'.

"The dog wagged its tail. (possessive)"
"It's been a long day. (= it has)"
"I have two cats. (plain plural, no apostrophe)"

Unnecessary commas and overused exclamation marks

English doesn't normally add a comma before 'that' introducing reported speech, or before 'because' when it introduces the main reason for something. And while one exclamation mark is fine for genuine excitement or urgency, stacking several (!!!) or writing in all capitals reads as shouting rather than emphasis in standard written English.

"He said that he was ready. (no comma)"
"She left early because she felt sick. (no comma)"
"I'm so excited about this trip! (one mark is enough)"

Real English

"The meeting ran long, so we rescheduled the call."
"I love this song! (not!!! — one is enough)"
"The cat licked its paw and went back to sleep."
"We bought two tickets, not two ticket's."

Watch out

✗The movie was long, we still enjoyed it.
✓The movie was long, but we still enjoyed it.

A comma alone can't join two full sentences — add a conjunction (but, so, and) or use a period.

✗The movie was long we still enjoyed it.
✓The movie was long, but we still enjoyed it.

With no punctuation at all between them, this is a run-on sentence — an even more common version of the comma splice problem.

✗The dog wagged it's tail and chased two cat's.
✓The dog wagged its tail and chased two cats.

Two separate traps in one sentence: 'its' (possessive) needs no apostrophe, and a plain plural ('cats') never takes one either.

Real life — A friend proofreading a cover letter

"Can you check this paragraph for me before I send it?"

"Sure — this sentence here is a comma splice: 'I finished the project early, I moved on to the next task.' It needs a conjunction or a period."

"Good catch. I'll write: 'I finished the project early, so I moved on to the next task.'"

"Much better — and watch out, you also wrote 'it's' here where you mean the possessive 'its'."

Practice

Exercise 1 · Choose the correctly fixed sentence

Which sentence fixes the comma splice correctly?

Exercise 2 · Choose the correctly fixed sentence

Which sentence fixes the run-on sentence correctly?

Exercise 3 · Choose the correct sentence

Which correctly avoids the its/it's mistake?

Exercise 4 · Choose the correct sentence

Which correctly avoids a plural-with-apostrophe mistake?

Exercise 5 · Choose the correct sentence

Which sentence avoids overusing exclamation marks?

Exercise 6 · Choose the correct sentence

Which sentence correctly avoids an unnecessary comma before 'because'?

Exercise 7 · Choose the correctly fixed sentence

Which correctly fixes a missing apostrophe in a possessive?

Exercise 8 · Fix the run-on sentence

Fix the run-on sentence: 'The movie was long we still enjoyed it.' (add a conjunction)

Exercise 9 · Choose the correct definition

What is a 'comma splice'?

Exercise 10 · Sort the sentences into groups

It was raining, I stayed inside.
It was raining, so I stayed inside.
The dog wagged it's tail.
The dog wagged its tail.

0 / 4 sorted

Quick challenge

Five quick questions to check what stuck.

Question 1 / 5

Score: 0/0

Which sentence is correct (no comma splice)?

You learned

  • A comma splice joins two full sentences with only a comma — add a conjunction or a period.
  • A run-on sentence joins two full sentences with no punctuation at all.
  • 'its' (no apostrophe) is possessive; 'it's' means 'it is/has'.
  • A plain plural never takes an apostrophe.
  • Skip the comma before 'that'/'because' introducing essential information, and use exclamation marks sparingly.

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Learn how to punctuate direct speech in English: quotation marks, capital letters, comma placement, and starting a new paragraph for each new speaker.

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Apostrophes

Learn the two jobs of the apostrophe in English: showing possession (Tom's book) and forming contractions (don't, it's) — plus the classic its/it's mix-up.

View all lessons in this category