Curriculum fit: KS3 and GCSE English Language (punctuation accuracy). US: Common Core ELA Language standards (conventions of standard English, grades 6-10).
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What Is It?
Apostrophes and commas are the punctuation marks that students misuse most often. Each has a small number of clear jobs, and learning them removes many common errors.
Apostrophes show missing letters (contractions) and possession. Commas separate items in a list, mark off introductory phrases and extra information, and join sentences with conjunctions.
Key Formulas and Ideas
- Contractions: don't = do not, it's = it is.
- Singular possession: add 's (the girl's book). Plural ending in s: add an apostrophe only (the girls' books).
- Its (possessive) never takes an apostrophe. It's always means 'it is' or 'it has'.
- Use a comma after an opening phrase and before a conjunction that joins two main clauses.
Worked Examples
Its or It's
Choose the correct word: 'The dog wagged ___ tail.'
- Replace the gap with 'it is': 'The dog wagged it is tail' does not make sense.
- So the possessive 'its' is needed.
✓ Answer its
Singular or Plural Possession
Write 'the books belonging to the girls' using an apostrophe.
- 'Girls' is plural and ends in s.
- Add just an apostrophe after the s.
✓ Answer the girls' books
Fix a Comma Splice
Fix: 'I was tired, I slept.'
- Two complete sentences are joined only by a comma.
- Add a conjunction, or use a full stop or semicolon.
✓ Answer I was tired, so I slept.
Common Mistakes to Avoid
- Writing 'it's' for the possessive.
- Using an apostrophe to make a simple plural (apple's).
- Missing the comma after an introductory phrase.
- Joining two sentences with only a comma.
Practice Questions
Frequently Asked Questions
How do I check its vs it's?
Replace it with 'it is'. If the sentence still makes sense, use it's. If not, use its.
How do I check its and it's?
Say 'it is' in its place. If the sentence still makes sense, use it's. If not, use its.
Keep Going With These Guides
Semicolons, Colons and Dashes: How to Use Them Correctly
Link ideas with semicolons, introduce lists with colons and add emphasis with dashes, with clear rules and examples.
GCSEHigh SchoolAPSimple, Compound and Complex Sentences Explained
Identify clauses and build simple, compound and complex sentences for clearer, more varied writing, with examples.
KS3GCSEMiddle SchoolHigh SchoolCommonly Confused Words: Their, There, Affect and Effect
Choose between their, there and they're, affect and effect, your and you're, and other mixed-up words, with a quick test for each pair.
KS3GCSEMiddle SchoolHigh SchoolSources and Review
- DfE: National curriculum in England, English programmes of study
- Common Core State Standards: English Language Arts and Literacy
Reviewed by StudyMorrow editorial review on 5 Nov 2026.