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.
ReviewedEvidence5 sourcesSectionWriting & Style
Quick answer
Do not use one universal preposition rule. APA 7 capitalizes words of four letters or more, including longer prepositions; Chicago 18 capitalizes prepositions of five letters or more; MLA’s published editorial guidance lowercases internal prepositions regardless of length, with first/last-position rules handled separately.
Key details
APA 74+ letters capitalized; short internal prepositions lowercase
Chicago 185+ letter prepositions capitalized; shorter internal prepositions lowercase
Mlainternal prepositions generally lowercase in MLA editorial guidance; full MLA 9 automatic treatment still under review
Rule Familyminor-words
Style-by-style guidance
APA 7
APA title case treats words of four letters or more as major words, so longer prepositions are capitalized while short prepositions are normally lowercase internally.
Chicago 18
Chicago 18 changed its prior rule and now capitalizes prepositions of five letters or more; shorter internal prepositions generally stay lowercase.
Mla
MLA’s detailed public guidance says internal prepositions remain lowercase regardless of length, but that specific article is edition-labeled for MLA 8. The current MLA 9 public handout independently confirms the first/last/principal-word framework.
Further guidance
Why This Matters
A converter that uses a single small-word list for every style will produce wrong output. This guide therefore stores preposition behavior by style profile rather than as one site-wide rule.
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.
Multiword prepositions such as “according to,” “because of,” “instead of,” “out of,” and “up to” should not be handled by a single crude small-word list. Different style systems analyze components differently, and some phrases contain words that can change grammatical role.
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.
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.
APA capitalizes “After” 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 “Against” internally because it has at least four letters. Chicago 18 also capitalizes it because prepositions of five letters or more are capitalized. MLA ordinarily lowercases internal prepositions, while any principal-word use needs grammatical classification before an automated decision.
APA capitalizes “Among” internally because it has at least four letters. Chicago 18 also capitalizes it because prepositions of five letters or more are capitalized. MLA ordinarily lowercases internal prepositions, while any principal-word use needs grammatical classification before an automated decision.
