“Of” is normally lowercase in the middle of a title in APA 7, Chicago 18, and MLA-style title capitalization because it is a short preposition. First- or last-word position can override the ordinary middle-of-title treatment.
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Quick answer
Usually no when “of” appears inside a title. APA treats the two-letter preposition as a short minor word; Chicago 18 lowercases internal prepositions of four letters or fewer; MLA editorial guidance also lowercases internal prepositions. Capitalize it when an applicable style requires capitalization because of position.
Key details
APA 7lowercase internally
Chicago 18lowercase internally
Mlalowercase internally in MLA editorial guidance
Normal Mid Title Formof
Termof
Word Classpreposition
Style-by-style guidance
APA 7
In APA 7, “of” has fewer than four letters and is normally lowercase as an internal minor word in title case.
Chicago 18
Chicago 18 now capitalizes prepositions of five letters or more, which leaves the two-letter “of” lowercase in ordinary internal position.
Mla
MLA editorial guidance treats internal prepositions as lowercase. The current ninth-edition public handout separately confirms that first and last words are capitalized.
Further guidance
Position Rule
Do not turn “of” into an always-lowercase token. The first or last word can be capitalized because position rules outrank the ordinary internal-preposition 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.
“To” is normally lowercase in the middle of titles under APA, Chicago, and MLA-style capitalization when it functions as a short preposition; Chicago also explicitly keeps “to” lowercase as an infinitive marker in ordinary mid-title position. Edge position can change the result.
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 “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.
Usually no in the middle of a title. “at” is a short preposition: APA lowercases short prepositions of three letters or fewer, Chicago 18 lowercases prepositions of four letters or fewer, and MLA title style normally treats internal prepositions as minor words. The answer depends on the style guide and position, so this page separates APA 7, Chicago 18, and MLA guidance instead of applying one generic title-case list.
