Prepositions in Title Case
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.
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
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
Practical Application
Choose preposition capitalization from the governing title style, not from one universal rule: APA 7 capitalizes words of four letters or more, Chicago 18 capitalizes prepositions of five letters or more, while MLA editorial guidance generally lowercases internal prepositions regardless of length.
Reader Check
Before capitalizing a preposition, identify the style and the word’s role and position. First/last-word rules and words functioning as other parts of speech can change the result.
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.
Worked Example
The same title may capitalize a longer preposition under APA or Chicago while lowercasing it under MLA. A title-case tool should therefore require the selected style before deciding.
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.
- Title case capitalization (opens in a new tab)American Psychological Association · APA title-case rules
- What's New in the 18th Edition (opens in a new tab)The Chicago Manual of Style / University of Chicago Press · Chicago 18 title-case terminology and five-letter-preposition change
- Headlines and Titles of Works — Chicago Q&A (opens in a new tab)The Chicago Manual of Style / University of Chicago Press · Chicago title-case rules and current-edition updates
- How should I capitalize the title of a handout? (opens in a new tab)MLA Style Center / Modern Language Association · MLA title-style capitalization
- In MLA style, should any part of a two-word preposition be capitalized in a title? (opens in a new tab)MLA Style Center / Modern Language Association · MLA editorial guidance on internal prepositions in titles