Punctuation Essentials: Commas, Apostrophes and Full Stops

You don't need to know every punctuation rule in English. A handful of them cause most of the problems in student writing.

Full stops and run-on sentences

Each sentence needs its own subject and verb, and ends with a full stop. Joining two sentences with only a comma is called a comma splice, and it's one of the most common errors at every level.

Commas: five uses that matter

1. After an introductory word or phrase: However, the plan failed. / In the morning, we left early.
2. In lists: We bought bread, cheese and olives. (The comma before and is optional in British English.)
3. Before but / so / or joining two full clauses: It was late, so we took a taxi.
4. Around extra information: My brother, who lives in Berlin, is a nurse.
5. After a subordinate clause at the start: Although it was raining, we went out. (But no comma when the order is reversed: We went out although it was raining.)

No comma before "that"

Apostrophes

Apostrophes do two jobs:

• Missing letters: it's (it is), don't (do not), I'll (I will)
• Possession: my sister's car, the students' books (more than one student)

Never use an apostrophe for a simple plural: photos, not photo's; the 1990s, not the 1990's.

Capital letters

Use capitals for: the first word of a sentence, I, names, places, nationalities and languages (Turkish, English), days and months (Monday, March). Not for seasons (summer) or school subjects, except languages (maths, history, French).

Question marks and exclamation marks

One is enough. Really?!! belongs in a text message, not in an essay. In formal writing, avoid exclamation marks almost completely.