"On" is one of the trickiest words in title capitalization because it can function as three different parts of speech. As a preposition, it stays lowercase in nearly every style guide. As an adverb or a particle in a phrasal verb, several guides capitalize it. Most writers default to lowercase and get away with it, but if you are writing a book title or an academic paper, the distinction matters.
This guide breaks down how Chicago, MLA, APA, AP, AMA, the New York Times, Wikipedia, and Bluebook each handle "on" in titles, including the cases where you should capitalize it.
Quick Reference: "On" by Style Guide
| Style Guide | Capitalize "On"? | Rule |
|---|---|---|
| Chicago (CMOS) | No (preposition); Yes (adverb) | Lowercase prepositions of any length; capitalize "on" when it functions as an adverb |
| APA (7th edition) | No | "On" has only 2 letters, below the 4-letter capitalization threshold |
| MLA | No | Lowercase prepositions regardless of length |
| AP (Associated Press) | No | Capitalize prepositions of 4+ letters; "on" is 2 letters |
| AMA | No | Lowercase prepositions and short articles |
| New York Times | No (preposition); Yes (adverb) | Same rule as Chicago: capitalize "on" when it acts as an adverb |
| Wikipedia | No (with exceptions) | Capitalize "on" inside a phrasal verb or as the first word of a compound preposition |
| Bluebook | No | Lowercase prepositions of 4 letters or fewer |
The takeaway: in almost every situation, "on" stays lowercase. The cases where it gets capitalized are listed in the when to capitalize section below.
What "On" Is Doing in Your Title
"On" is most commonly a preposition (it shows the relationship between two things) but it can also function as:
"On" is most commonly a preposition, showing the relationship between two things. It also functions as an adverb, the way "on" modifies "carry" in Carry On. It shows up as a particle in phrasal verbs like Move On, Hold On, and Switch On. Less commonly, it acts as an adjective describing a state, as in The Lights On. The grammatical role decides what to capitalize in stricter style guides like Chicago, the New York Times, and Wikipedia.
The grammatical role decides what to capitalize in stricter style guides like Chicago, the New York Times, and Wikipedia. AP, APA, AMA, MLA, and Bluebook lowercase "on" no matter what, because their rules are length-based or category-based without exceptions for adverbs.
Chicago Manual of Style
Chicago's headline-style capitalization keeps prepositions lowercase regardless of length. "On" stays lowercase as a preposition.
The important exception: when "on" is functioning as an adverb or a particle in a phrasal verb, Chicago treats it as a principal word and capitalizes it. Compare:
- Notes on a Scandal: "on" is a preposition, lowercase.
- Keep On Running: "on" is an adverb inside the phrasal verb "keep on", capitalized.
MLA Style
MLA matches Chicago on prepositions: lowercase regardless of length. "On" stays lowercase unless it is the first word, the last word, or directly follows a colon. MLA does not make the adverb distinction as explicitly as Chicago, but most academic editors treat phrasal-verb "on" as capitalized in MLA contexts too.
APA Style
APA capitalizes words of four or more letters and lowercases all others. Because "on" is only two letters, it stays lowercase in mid-title position regardless of grammatical role. The exception, as always, is when "on" is the first word of the title, the first word of a subtitle (after a colon), or the last word.
For the full APA breakdown, see the APA title case rules guide.
AP Style
AP capitalizes prepositions of four letters or more. "On" is two letters, so AP keeps it lowercase. Most American newsrooms follow AP, which is why you almost never see "On" capitalized in a news headline.
AMA Style
The American Medical Association style guide, used in medical and health journals, lowercases prepositions and short articles in titles. "On" is lowercase under AMA unless it is the first or last word.
New York Times Style
The Times follows the same logic as Chicago: lowercase "on" when it is a preposition, capitalize it when it is an adverb or part of a phrasal verb. The Times also capitalizes any preposition that is four or more letters when it is the first or last word.
Wikipedia Manual of Style
Wikipedia's article-title rules lowercase "on" as a preposition. There are two specific exceptions where Wikipedia capitalizes it:
- When "on" is part of a phrasal verb, e.g., The Sun Also Rises On.
- When "on" is the first word of a compound preposition, e.g., On Behalf Of the Crown.
Bluebook (Legal Writing)
Bluebook, the standard for legal citations and briefs, lowercases prepositions of four letters or fewer. "On" stays lowercase in case names, brief titles, and law-review article titles unless it leads the title or follows a colon.
When to Capitalize "On"
Across every style guide above, "on" gets capitalized in these specific cases:
Across every style guide above, "on" gets capitalized when it appears as the first word of the title, like On the Origin of Species by Charles Darwin. It is also capitalized when it is the last word, or when it follows a colon or dash that introduces a subtitle, as in A Cultural History: On the Edge. Chicago, the New York Times, and Wikipedia capitalize "on" when it functions as an adverb or sits inside a phrasal verb, so titles like Carry On and Move On take a capital. Wikipedia also capitalizes "on" when it leads a compound preposition like On Behalf Of the Court.
Real Titles That Use "On"
- On the Road by Jack Kerouac, "On" capitalized as the first word.
- Notes on a Scandal by Zoë Heller, "on" lowercase as a mid-title preposition.
- Carry On by Rainbow Rowell, "On" capitalized as the last word and as an adverb.
- Reflections on the Revolution in France by Edmund Burke, "on" lowercase as a preposition.
- The Sun Also Rises (not Rises On), illustrates the lowercase default when "on" is not actually in the title.
Common Mistakes
Writers most often go wrong by capitalizing "on" everywhere because they assume any word over two letters needs a capital. It does not. In Chicago, MLA, and most other guides, "on" stays lowercase mid-title when it is acting as a preposition. The flip side is missing Chicago's adverb exception: when "on" is part of a phrasal verb like Keep On Running, Chicago does capitalize it. The colon rule trips people up too, because every guide capitalizes the first word after a colon even when that word is "on."
Apply the Rules Automatically
If you do not want to memorize every guide, paste your title into the free title case converter at the top of the page. Pick your style (Chicago, AP, APA, MLA, or others) and the tool applies the rules above instantly, including the lowercase "on" treatment.
