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.
ReviewedEvidence3 sourcesSectionWriting & Style
Quick answer
Capitalize the first word of a subtitle even when that word would normally be minor. APA states this directly; Chicago applies title-case rules after the colon separating a title and subtitle; MLA’s public Style Center has likewise shown articles capitalized at the start of subtitles, although the cited public post is edition-labeled for MLA 8.
Key details
APA 7capitalize first word of subtitle / after qualifying title punctuation
Chicagocapitalize first word after title/subtitle colon
Mlapublic Style Center example supports subtitle-initial capitalization; current automated profile requires manual review
Rule Familyboundaries
Style-by-style guidance
APA 7
APA title case capitalizes the first word of a subtitle and the first word after a colon, em dash, or end punctuation in a heading.
Chicago
Chicago treats the word after the colon that separates a title and subtitle as a title-case boundary and capitalizes it.
Important caveats
Automation boundary
A converter must recognize subtitle and punctuation boundaries before applying minor-word rules; punctuation cannot be discarded during tokenization.
Further guidance
Mla Public Guidance
MLA’s Style Center shows articles such as “The” capitalized when they begin a subtitle. The available public article is explicitly tied to the eighth edition, so automated MLA 9 coverage remains conservative.
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.
Hyphenated compounds cannot be capitalized safely with one universal “capitalize everything after a hyphen” rule. APA explicitly capitalizes the second part of hyphenated major words, while Chicago 18 changed its prefix-compound treatment and still applies grammatical title-case rules to individual elements.
APA title case capitalizes the first word, the first word of a subtitle, major words, and words of four letters or more while keeping short minor words lowercase in ordinary mid-title positions.
Chicago 18 uses title case for titles of works and changed a long-standing rule: prepositions of five letters or more are now capitalized. Shorter prepositions generally remain lowercase internally, while first and last words are capitalized and “to” remains lowercase as an infinitive marker in ordinary mid-title use.
MLA 9 describes title style as capitalizing the first word, last word, and all principal words. MLA’s public Style Center also documents the traditional lowercase treatment of internal prepositions, but its detailed preposition article is edition-labeled for MLA 8, so this engine does not yet treat the full MLA 9 converter profile as complete.
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.
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.
Short words such as “up,” “out,” and “on” can change capitalization when their grammatical role changes. Chicago’s own examples capitalize “Up” or “Out” when those words function adverbially in a phrasal verb, while ordinary prepositional uses can remain lowercase.
