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Grammar

Punctuation for Readability

Commas, semicolons, apostrophes and capital letters used correctly make your writing clear and professional — and directly support your Readability score.

6 min read · Updated June 18, 2026 · By the Celpip.me editorial team · Free
Quick answer
Updated Sep 16, 2026

Punctuation is scored under CELPIP Readability, so correct commas, semicolons, and apostrophes make your writing look professional. The apostrophe has two jobs: showing possession (the dog's bone) and contraction (it's = it is). Add a comma after an introductory phrase and before and/but/so joining two full sentences; use a semicolon to join two closely related complete sentences instead.

What's the difference between "its" and "it's"?
"Its" (no apostrophe) is possessive, as in "The dog wagged its tail." "It's" is a contraction meaning "it is," as in "it's happy."
When do I need a comma before "and," "but," or "so"?
Add a comma before and/but/so when it joins two full sentences, for example "I called twice, but no one answered."
What else besides the first word of a sentence needs a capital letter?
Capitalise the pronoun I, names, days and months, and countries and languages, such as English, Canada, and French.
Practice this with the free full mock →
Key strategies
  • 1.Use a comma after an introductory phrase: "After the meeting, we left." and before and/but/so joining two full sentences.
  • 2.A semicolon joins two closely related complete sentences: "It was late; we went home."
  • 3.Apostrophes show possession (the dog's bone) or contraction (it's = it is). "its" (no apostrophe) is possessive.
  • 4.Capitalise sentence starts, the pronoun I, names, days, months, and countries/languages.

Commas — the high-value ones

  • After an introductory phrase or clause:
    • "After lunch, we continued. Although it was hard, we finished."
  • Before a coordinator (and, but, so) joining two full sentences:
    • "I called twice, but no one answered."
  • Around extra (non-essential) information:
    • "My manager, who is very fair, approved it."
  • Between items in a list: "apples, pears, and grapes."

Semicolons and colons

  • Semicolon (;) joins two closely related complete sentences without a connector:
    • "The deadline passed; nothing was ready."
  • Colon (:) introduces a list or an explanation:
    • "We need three things: time, money, and focus."

The apostrophe — two jobs

  • Possession: "the company's policy", "the students' results".
  • Contraction: "it's" = it is; "they're" = they are.

Watch the classic trap: its (possessive, no apostrophe) vs. it's (it is).

✓ "The dog wagged its tail because it's happy."

Capital letters

Capitalise: the first word of a sentence, the pronoun I, names, days/months, countries and languages (English, Canada, French).

CELPIP application

Punctuation is part of Readability. Correct commas and apostrophes make sentences easy to parse; errors (a missing apostrophe, a comma splice) are small but visible signals to the rater.

Check yourself

A quick self-check on this lesson — pick an answer, then see the explanation. Not graded.

1. Choose the correctly punctuated sentence:
2. Which uses "its / it's" correctly?
3. Correct possessive:
4. Which correctly joins two complete sentences with a semicolon?

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