APA capitalizes “Under” internally because it has at least four letters. Chicago 18 also capitalizes it when used as a preposition because current Chicago capitalizes prepositions of five letters or more. MLA treatment still depends on grammatical function, so prepositional and principal-word uses should not be collapsed into one rule.
ReviewedEvidence6 sourcesSectionWriting & Style
Quick answer
APA: capitalize. Chicago 18: capitalize. MLA: normally lowercase when “under” is a preposition, but capitalize a principal-word use; first/last-word rules can override ordinary internal treatment.
Key details
APA 7Capitalize internally because it has five letters.
Automation NoteBoundary rules override ordinary internal treatment. MLA role-sensitive uses remain review-only unless the phrase structure is established safely.
Chicago 18Capitalize internally; Chicago 18 capitalizes prepositions of five letters or more and principal words.
MLA 9Lowercase as a preposition; capitalize principal-word uses such as adverbs/adjectives.
TermUnder
Word Classpreposition / adverb / adjective
Style-by-style guidance
APA 7
Capitalize internally because it has five letters.
Chicago 18
Capitalize internally; Chicago 18 capitalizes prepositions of five letters or more and principal words.
MLA 9
Lowercase as a preposition; capitalize principal-word uses such as adverbs/adjectives.
Important caveats
Automation boundary
APA and current Chicago are deterministic for this spelling in ordinary internal position, but MLA still requires grammatical-role awareness. Multiword-preposition recognition is treated as structure metadata, not as permission to guess.
Further guidance
Quick rule
APA: capitalize. Chicago 18: capitalize. MLA: normally lowercase when “under” is a preposition, but capitalize a principal-word use; first/last-word rules can override ordinary internal treatment.
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.
Prepositions are one of the clearest places where title styles diverge. APA uses a four-letter major-word threshold, Chicago 18 capitalizes prepositions of five letters or more, and MLA editorial guidance generally lowercases internal prepositions regardless of length.
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.
APA capitalizes “Near” internally because it has four letters. Chicago 18 lowercases it when it is a short preposition but capitalizes adverb/adjective uses; MLA likewise distinguishes minor-preposition from principal-word uses. This guide keeps style-specific rules separate and marks grammatical ambiguity where the same spelling can play different roles.
APA capitalizes “Through” internally because it has at least four letters. Chicago 18 also capitalizes it when used as a preposition because current Chicago capitalizes prepositions of five letters or more. MLA treatment still depends on grammatical function, so prepositional and principal-word uses should not be collapsed into one rule.
APA capitalizes “About” internally because it has at least four letters. Chicago 18 also capitalizes it when used as a preposition because current Chicago capitalizes prepositions of five letters or more. MLA treatment still depends on grammatical function, so prepositional and principal-word uses should not be collapsed into one rule.
APA capitalizes “Across” internally because it has at least four letters. Chicago 18 also capitalizes it when used as a preposition because current Chicago capitalizes prepositions of five letters or more. MLA treatment still depends on grammatical function, so prepositional and principal-word uses should not be collapsed into one rule.
