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Definition: a punctuation mark (:) used to precede a list of items, a quotation, or an expansion or explanation.

Note: Do not rely on grammar or spelling checkers to identify missing or misused punctuation. Although a checker may flag possibly missing or incorrect marks, it cannot do much else. While I still recommend using these AI checkers while you’re writing, I insist that you also trust a qualified human being to copyedit any work that you are working toward publishing.

There are three main uses for a colon: to introduce a list, statement, quotation, or summary; to introduce a clause relating to the preceding clause; and to indicate typographic distinctions. Essentially, it means “Here they are.”

To Introduce a List, Statement, Quotation, or Summary:

Use a colon after the word follows or following.

• e.g. I set about packing the following for vacation: clothes, books, swimsuits, and sunscreen.

Never use a colon after a form of the verb to be.

• e.g. Some of my favourite books are Harry Potter and the Prisoner of Azkaban, Dracula, The Hunger Games, and The Lightning Thief.

Use a colon to introduce a formal or lengthy statement or quotation, or in headlines to introduce an idea.

• e.g. Dumbledore held up his hand before addressing the students: “To our new students, welcome to Hogwarts…”
• e.g. Oilers Notes: Nugent-Hopkins happy for former teammate

If the second word group summarizes the first, introduce it with a colon.

• e.g. Henry was the best hiker in the group: twenty years of experience spoke for itself.

To Relate One Clause to a Previous One:

Use a colon to emphasize an explanatory relationship between two clauses.

• e.g. Greg didn’t want to go to boarding school: His father forced him to.

If the relationship seems minor, use a semicolon instead of a colon.

• e.g. Sebastian joined the orchestra; there were three other violinists.

Typographically:

Use a colon (without spaces) between chapter and verse in references to the Bible.

• e.g. Proverbs 28:20

Use a colon (with no spaces) between the hour and minutes in time designations.

• e.g. 12:20

Use a colon (space after but not before) between the volume number and page number in a bibliographic reference even if the year appears within parentheses between the two.

• e.g. Journal of Sociology 4 (1979): 325–339.

Use a colon between the city and the publisher in bibliographic references.

• e.g. Indianapolis, IN: Bobbs-Merrill

Use a colon between a title and a subtitle.

• e.g. Cathy followed all the instructions in “Green Thumbs: Growing Herbs for Beginners,” but the plants still died.

Use a colon in play dialogue, following speakers’ names. Some publishers use a different typographic system for plays, but the general consensus is to use a colon.

• e.g. TIMOTHY: Where are you going? / MAY: To put an end to this.

With Other Punctuation:

A colon goes outside an end quotation mark.

• e.g. Students filtered into the courtyard from all classes: Potions, Herbology, Transfiguration, Divination.

A colon never precedes a parenthesis (except typographically).

• e.g. They heard from Little Danny (a pure soul if there ever was one): “I want to be a doctor to help people.”

For further information, see my other Punctuation articles:

Sources:

Aaron, J.E. & Morrison, A. The Little, Brown Compact Handbook, 5th Canadian ed. Pearson, 2013, chap 5

Judd, K. Copyediting, A Practical Guide, 3th ed. California, CA: Crisp Learning, 2001, chap 4