Chicago 18 changed how later elements in prefix-based hyphenated compounds are capitalized: each component now follows the general title-case rule. Safe automatic treatment still requires recognizing that the hyphen truly joins a reviewed prefix compound.
ReviewedEvidence4 sourcesSectionWriting & Style
Quick answer
In Chicago 18, a retained hyphen in a prefix-based compound no longer automatically forces a lowercase second element. Reviewed examples support forms such as “Co-Founder” and the 18th-edition pattern “Anti-Intellectual.”
Key details
Automation Statussafe only for reviewed prefix patterns
Rule Familyhyphenated-compounds
Style ScopeChicago 18
Important caveats
Automation boundary
Reviewed prefix patterns can be handled consistently, but arbitrary hyphenated compounds should not be assumed to be prefix compounds.
Further guidance
Chicago 18 Rule
Chicago’s 18th-edition change summary says later elements in a hyphenated term beginning with a prefix are capitalized according to the general title-capitalization rule.
Reviewed Prefixes
Chicago’s Q&A supplies reviewed prefix-compound examples including co-founder, anti-intellectual, pro-life/pro-choice, sub-Saharan, and pre-1950 forms.
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.
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.
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.
Some names and work titles intentionally use distinctive casing or punctuation that a generic title-case algorithm should not normalize away. A safe converter needs a reviewed preservation layer and must distinguish a known protected form from arbitrary mixed case.
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.
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.”
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.
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.
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.
