Punctuation & Capitalization

Basic · Writing Mechanics

Punctuation is the traffic signal system of writing: it tells the reader when to pause, stop, or notice something. Correct punctuation and capital letters make your writing clear and professional.

These are the essential rules that cover the vast majority of everyday writing.

Rules & examples

1. Capital letters: sentence starts, the word "I", names, places, days, months, nationalities.

   Proper nouns and "I" are always capitalized.

   • I met John on Monday in France.
2. A full stop (period) ends a statement; a question mark ends a question.

   Each sentence needs its end mark.

   • She is here.
   • Where is she?
3. Commas separate items in a list and mark off clauses.

   They create natural pauses and prevent confusion.

   • I bought apples, bread, and milk.
   • When it rains, I stay in.
4. Apostrophes show possession or contractions.

   Two jobs: ownership (Sara's) and short forms (don't).

   • Sara's book
   • don't = do not
5. Do NOT use an apostrophe to make a plural.

   Plurals just add -s, with no apostrophe.

   • I have three cats. (not: cat's)

Tips to remember

• its (belonging to it) has NO apostrophe; it's (it is) HAS one. This is the most common apostrophe error in English.
• Always capitalize the pronoun "I", wherever it appears in a sentence.

Common mistakes

• ✗ i live in london. → ✓ I live in London. — Capitalize "I" and proper nouns like city names.
• ✗ The dog wagged it's tail. → ✓ The dog wagged its tail. — "Its" is possessive; "it's" means "it is".