Writing & StyleRule guide

Nested Subtitles and Colons in Title Case

A colon can create a title/subtitle boundary, but nested punctuation still needs structural handling. Chicago capitalizes the first word after a title/subtitle colon; repeated or nested colons should therefore be parsed as boundaries rather than treated as ordinary word punctuation.

Reviewed2026-09-28Evidence4 sourcesSectionWriting & Style

Quick answer

In title case, capitalize the first word after a genuine title/subtitle colon. If a title contains more than one colon, each reviewed structural boundary can restart capitalization, but an automatic tool should not assume every colon has the same semantic role.

Key details

Automation Statussafe only when structural role is reviewed

Boundarycolon

Rule Familysubtitle-boundaries

Important caveats

Automation boundary

A colon inside an embedded quotation or unresolved protected title remains structural and may still leave the result unresolved.

Subtitle Boundary

Chicago’s title-case guidance capitalizes the first word after the colon that separates a title from a subtitle.

Further guidance

Nested Colons

This guide tracks repeated colon boundaries independently so a second reviewed subtitle-like segment can restart title capitalization without losing the first boundary.

Practical Application

Treat a genuine colon between title/subtitle units as a structural boundary and capitalize the first word after it under the selected title-case rule. With multiple colons, parse the hierarchy first; do not assume every colon automatically starts a new subtitle.

Reader Check

Does each colon actually divide title/subtitle structure, or is one colon serving another grammatical or data-like function?

Worked Example

For the reviewed structural pattern “A Guide: Rules: Examples,” each genuine subtitle boundary can restart first-word capitalization. An automated converter should fail closed when it cannot determine that a colon is structural.

Sources and evidence

Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.

Headlines and Titles of Works — Chicago Q&A (opens in a new tab)The Chicago Manual of Style / University of Chicago Press · Chicago title-case rules and current-edition updates
Title case capitalization (opens in a new tab)American Psychological Association · APA title-case rules
How should I capitalize the title of a handout? (opens in a new tab)MLA Style Center / Modern Language Association · MLA title-style capitalization
Headlines and Titles of Works — capitalization after a colon in title case (opens in a new tab)The Chicago Manual of Style / University of Chicago Press · Chicago title/subtitle boundary rule

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Parentheses can appear in headings and titles without creating a new capitalization system. Chicago says the parentheses themselves are normally ignored when title case is applied, so words inside still follow their grammatical title-case rules.

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The first word of a subtitle is treated as a new capitalization boundary in major title-case systems. APA explicitly capitalizes the first word of a subtitle, Chicago capitalizes the word after a title/subtitle colon, and MLA has published the same treatment in its Style Center guidance.

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Embedded Titles in Title Case

A title appearing inside another title has its own identity and may need quotation marks, italics, or language-specific treatment. Flattening the inner title into the outer title’s token stream can destroy both formatting and capitalization.

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Capitalization Title Case Punctuation