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.
ReviewedEvidence4 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.
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.
Major title-case systems capitalize the first and last words of a title or subtitle even when the same word would normally be lowercase internally. A converter therefore needs segment endpoints, not only a small-word list.
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.
Colons, semicolons, and dashes can create capitalization boundaries in titles, while quotation marks and parentheses may introduce embedded structures that require additional analysis. This guide separates punctuation-boundary detection from word-class decisions so it can explain when a new segment begins and when it must leave the result unresolved.
Quotation marks do not by themselves decide which words are capitalized. A converter must distinguish harmless outer quotation punctuation from an embedded title or quoted structure that may need its own capitalization and formatting rules.
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.
Apostrophes can mark possession, contractions, or omitted initial letters, and those uses should not be confused with quotation marks. Chicago also has specific title-case examples for initial-apostrophe contractions and for the compound form “O’Clock.”
Hyphens and dashes are not interchangeable in title-case logic. Chicago 18 changed the treatment of later elements in prefix-based hyphenated compounds, while an em dash can act like a parenthetical or subtitle-like boundary depending on structure.
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.
