Punctuation organises meaning. The same words, punctuated differently, can shift from a statement to a question, from one idea to two, from a possessive to a plural. This lesson covers the three marks that do most of that work in everyday writing: the sentence-ending marks, the comma, and the apostrophe.
Sentence endings
Three marks close a sentence, and each signals a different intention.
| MARK | USE |
|---|---|
| . period | ends a statement |
| ? question mark | ends a direct question |
| ! exclamation mark | signals strong emotion |
A period is the default. Use it for any statement, including polite requests shaped like questions (Could you send the file when you have a moment. is acceptable in formal contexts, though a question mark is more common).
A question mark belongs only to direct questions — the sentence actually asks something. An indirect question reports a question inside a statement, and it takes a period.
The second sentence is a statement about what the speaker wonders, not a question addressed to anyone.
Exclamation marks signal surprise, urgency, or strong emotion. In formal writing, use them sparingly — one per page is already a lot. Stacking them (Amazing!!!) reads as unserious.
Commas
Commas are the most frequently misused mark in English because they do several different jobs. The six uses below cover almost everything a learner needs.
In lists
Separate three or more items with commas.
The final comma before and (the Oxford comma) is optional, but this course uses it consistently. It prevents ambiguity: I invited my parents, Beyoncé and Obama reads very differently from I invited my parents, Beyoncé, and Obama.
After an introductory phrase
When a sentence opens with a phrase that sets the scene — time, place, condition — put a comma after it before the main clause starts.
Short introductory phrases of two or three words sometimes appear without a comma in informal writing, but the comma is always safe.
Before *and*, *but*, *or* joining two full sentences
When two independent clauses (each with its own subject and verb, each able to stand alone) are joined by and, but, or, so, put a comma before the conjunction.
No comma is needed when the conjunction simply joins two verbs sharing the same subject: She called and left a message.
Joining two full sentences with only a comma — no conjunction — creates a comma splice: She called, I didn't answer. Use a period, a semicolon, or add but.
With direct address
When you name the person you're speaking to, set the name off with a comma.
Omitting the comma changes the meaning. Let's eat, Grandma invites Grandma to dinner; Let's eat Grandma suggests something much darker.
Around non-essential information
Information that could be removed without changing the core meaning of the sentence is set off with commas on both sides.
If the information is essential to identify what you're talking about, no commas: The woman who lives next door is a doctor. Here who lives next door tells us which woman — it can't be removed.
Between adjectives that independently describe a noun
When two adjectives both modify the noun equally and independently, separate them with a comma.
A quick test: if you can reverse the order (a modern, bright office) or insert and (bright and modern) and the phrase still sounds natural, use a comma. If not — a bright red car — no comma, because red pairs tightly with car and bright modifies the whole unit.
Commas also appear in conditional sentences, relative clauses, and with linking words like however and for example. Those patterns are covered separately.
Apostrophes
The apostrophe has two jobs: it marks contractions and it marks possession.
Contractions
An apostrophe replaces missing letters when two words merge.
| FULL FORM | CONTRACTION |
|---|---|
| do not | don't |
| it is / it has | it's |
| she is / she has | she's |
| we are | we're |
| cannot | can't |
| will not | won't |
| I am | I'm |
Contractions are standard in all but the most formal writing. Avoid them in legal documents and academic papers; use them freely in everything else.
Possession
To show that something belongs to someone, add 's to the owner's name.
For plural nouns ending in s, add only an apostrophe after the existing s.
For plural nouns not ending in s (children, people, women, men), add 's normally.
Singular names that already end in s (James, Chris, Dickens) accept either James's book or James' book. Both are correct; pick one style and stick with it.
*Its* versus *it's*
This is the single most common apostrophe mistake in English, and it runs opposite to the normal rule.
- it's = it is or it has (contraction)
- its = belonging to it (possessive, no apostrophe)
The logic: possessive pronouns — his, hers, ours, theirs, yours, its — never take an apostrophe. The apostrophe in it's is always a contraction.
Apostrophes do not make plurals
Never use an apostrophe to form a plural noun.
This is known as the "greengrocer's apostrophe" because it so often appears on hand-written shop signs: Tomato's £1. It is always wrong.
Common mistakes
Its vs it's
Comma splices
Missing comma after introductory phrase
Apostrophes in plurals
Question mark on indirect questions
Missing comma with direct address