Colons introduce subtitles, lists, definitions, and clarifications. Whether you capitalize the word that follows depends partly on the style guide you follow and partly on whether what follows is a complete clause.

This is one of those small rules that varies subtly between style guides and contexts. Getting it right is a quiet signal of careful writing. Here's the complete picture.

The basic rule for titles

In a title, the word after a colon is almost always capitalized, regardless of what type of word it is. This is unanimous across AP, Chicago, APA, MLA, NYTimes, Wikipedia, Bluebook, and AMA.

Examples:

  • The Truth: It's Not What You Think
  • On Writing: A Memoir of the Craft
  • Beyond Good and Evil: A Philosophy
  • To Save Everything, Click Here: The Folly of Technological Solutionism
  • Sapiens: A Brief History of Humankind

The colon in titles typically introduces a subtitle — a fuller explanation, a clarifying phrase, or an explicit subject. Because the subtitle is essentially its own mini-title with its own first word, it follows the first-word capitalization rule of any title-case style.

The basic rule for body text

In body text (paragraphs, articles, essays), the rules are more nuanced and depend on the style guide.

Chicago Manual of Style

Chicago says: capitalize the first word after a colon only if what follows is a complete sentence or has at least two independent clauses. If what follows is a single word, phrase, or list, lowercase it.

Chicago examples (correct):

  • The problem is simple: there isn't enough time. (capitalize There? No — single clause that's not a quotation)
  • Actually, per Chicago specifically: The problem is simple: there isn't enough time. (lowercase)
  • The team faced two choices: They could ship now and risk bugs, or they could delay and miss the launch window. (capitalize They — multiple independent clauses follow)
  • Three things matter: speed, accuracy, and clarity. (lowercase — list, not a sentence)

Chicago's logic: a colon introducing a single clause is functionally similar to a comma, so no new sentence starts. A colon introducing multiple clauses or a complete thought is functionally similar to a period.

AP Stylebook

AP is simpler: capitalize the first word after a colon if a complete sentence follows. Lowercase it otherwise.

AP examples (correct):

  • He gave one warning: Don't make me repeat myself. (capitalize — complete sentence follows)
  • The recipe calls for three things: flour, water, and salt. (lowercase — list)
  • I have only one rule: never write angry. (lowercase under AP — single clause without a subject, often debated)

AP's rule is the most common in journalism. It's straightforward to apply: if what follows could stand alone as a sentence, capitalize. Otherwise, lowercase.

APA

APA mostly follows Chicago's rule for body text, with one modern simplification: capitalize the first word after a colon if what follows is a complete sentence.

MLA

MLA follows the same pattern as Chicago.

The "list after colon" rule

When a colon introduces a list, the items are almost always lowercase (unless they're proper nouns). This is unanimous across style guides:

  • The kit includes three items: a hammer, a screwdriver, and a wrench.
  • Several countries voted yes: France, Germany, and Spain. (proper nouns capitalized — but they would be regardless)
  • Pick your top priority: speed, quality, or cost.

The same is true for vertical (bulleted) lists. The list items are usually capitalized as sentence fragments — but whether to capitalize their first letter depends on whether they're complete sentences or partial phrases.

The "definition after colon" rule

When a colon introduces a definition, the first word after is usually lowercase across all major style guides:

  • Convergence: the act of coming together to a single point.
  • Title case: a capitalization style that capitalizes most major words.
  • Heuristic: a practical rule of thumb rather than a strict procedure.

The capitalized form (Convergence: The act…) reads as a title rather than a definition. Reserve capitalization for cases where the post-colon material is functioning as a subtitle.

The "quoted text after colon" rule

When a colon introduces a quotation, the first word of the quotation follows whatever capitalization it originally had:

  • She said one thing: "I'm not going back." (Capitalized — the quotation starts with a capital because it's a complete sentence in the original.)
  • He whispered: "just one more day." (Lowercase if the original was lowercase, though this is rare in modern writing.)

For quotations that didn't have a clear first-letter case in the original (e.g., partial quotes), capitalize if the quoted material forms a complete sentence in your text.

The "subordinate clause after colon" rule

This is where it gets tricky. A subordinate clause (one that can't stand alone) after a colon stays lowercase under all style guides:

  • I knew the answer: that we'd been wrong from the start.
  • The conclusion was clear: that we needed to start over.

Even though these have subjects and verbs, the that at the start makes them subordinate clauses — they can't stand alone as sentences. So lowercase.

The exception: emphasizing the post-colon material

Sometimes writers intentionally capitalize the first word after a colon to give it emphasis or to suggest that what follows is its own distinct thought, almost like a heading inline with the text:

  • Here's the one rule that matters: Don't lie. (Capitalized for emphasis even though "Don't lie" could be argued as just a phrase.)
  • The lesson was simple: Move fast, ship often.

This usage is more common in journalistic writing and casual essays. Formal academic writing usually sticks to the strict rule. If you're writing in a publication with a defined style guide, follow what the guide says rather than what feels right.

Practical guidance for non-experts

If you don't want to memorize seven different style-guide rules, this approach works in most modern English contexts:

  1. In a title: capitalize the first word after a colon. Always.
  2. In body text, if a complete sentence follows the colon: capitalize.
  3. In body text, if a list, phrase, or single clause follows: lowercase.
  4. In definitions: lowercase.
  5. In quotations: follow the original capitalization (usually capitalized).

This isn't strictly Chicago, AP, or APA — but it produces output that all three styles would accept as correct in most circumstances.

The semicolon difference

A semicolon (rather than a colon) never gets a capitalized word after it. Semicolons connect two independent clauses, but the second clause doesn't restart capitalization:

  • I came; I saw; I conquered. (Each clause after the semicolon starts lowercase.)
  • The team worked late; the deadline approached.

So if you're choosing between a colon and a semicolon and you want to avoid the capitalization question, a semicolon sidesteps it entirely. (But use the right one for the meaning, not the punctuation rule.)

The em-dash difference

An em-dash also never gets a capitalized word after it (in standard usage). Em-dashes set off parenthetical material, but they don't end one sentence and start another the way a period or colon might:

  • The team — exhausted from weeks of work — finally shipped.
  • One thing matters most — speed.

So colon, semicolon, and em-dash all introduce material differently, and only the colon plus a complete sentence triggers post-punctuation capitalization.

Testing the rule

If you're not sure whether to capitalize after a particular colon, try this test: can the material after the colon stand alone as a complete sentence?

  • "There isn't enough time." — Yes, this is a complete sentence. So you'd capitalize: The problem is simple: There isn't enough time. (Under AP. Under Chicago, you'd lowercase if it's the only clause that follows.)
  • "Flour, water, and salt." — No, this is a list/fragment. Lowercase: The recipe calls for three things: flour, water, and salt.
  • "The act of coming together." — No, this is a noun phrase. Lowercase: Convergence: the act of coming together.

If you apply this test consistently, your colon-capitalization will be defensible under any major style guide — even if it doesn't exactly match one specific guide's rule.