"Under" is a 5-letter preposition, which puts it on the fault line that divides the major style guides. Chicago and MLA keep "under" lowercase no matter how long it is. APA, AP, AMA, and the New York Times capitalize it because it has more than three letters. That one split answers almost every "under" question.
This guide breaks down the rule for "under" across eight style guides, with real examples and the mistakes that produce inconsistent titles.
Quick Answer
The rule for "under" depends on the style guide. In Chicago and MLA, keep "under" lowercase in a title unless it is the first or last word, because both guides lowercase prepositions of any length. In APA, AP, AMA, and the New York Times, capitalize "Under" mid-title because all four capitalize words of four or more letters. "Under" has five letters, so it clears every length threshold in use.
You can apply this automatically by pasting your title into the title case converter at the top of the page and choosing your style.
Quick Reference: "Under" by Style Guide
| Style Guide | Capitalize "Under"? | Rule |
|---|---|---|
| Chicago (CMOS) | No | Lowercase prepositions of any length |
| MLA | No | Lowercase prepositions regardless of length |
| APA (7th edition) | Yes | Capitalize words of 4 or more letters |
| AP (Associated Press) | Yes | Capitalize prepositions of 4 or more letters |
| AMA | Yes | Capitalize words of 4 or more letters |
| New York Times | Yes | Capitalize prepositions of 4 or more letters |
| Wikipedia | Yes | Capitalize prepositions of 5 or more letters |
| Bluebook | Yes | Capitalize prepositions of 5 or more letters |
Why Style Guides Disagree on "Under"
Title-case guides fall into two camps. Length-based guides capitalize any preposition over a set letter count: APA, AP, AMA, and the New York Times use a 4-letter cutoff, while Wikipedia and Bluebook use a 5-letter cutoff. "Under" is five letters, so it gets capitalized under all of them. Category-based guides like Chicago and MLA lowercase every preposition regardless of length, on the logic that prepositions are grammatical connective tissue and should not compete with nouns and verbs for emphasis. For the full picture, see title case prepositions: the 1 to 4 letter rule.
Chicago and MLA
Both Chicago and MLA keep "under" lowercase in the middle of a title. The World under Our Feet is correct Chicago style. The exception in both guides is position: capitalize "Under" when it is the first word, the last word, or directly follows a colon that introduces a subtitle.
APA, AP, AMA, and NYT
All four length-based guides capitalize "Under" because it passes the four-letter threshold. Working Under Pressure is correct in AP and APA. A Study Under Controlled Conditions capitalizes "Under" in any of these styles. For the full APA breakdown, see the APA title case rules.
Wikipedia and Bluebook
Wikipedia and Bluebook use a 5-letter cutoff for prepositions. "Under" has exactly five letters, which puts it in the capitalized group for both. A Wikipedia article title or a legal brief heading capitalizes "Under" in any position.
When to Capitalize "Under" in Any Style
Regardless of guide, capitalize "Under" when it is the first word of the title (Under the Tuscan Sun), the last word of the title, or the first word of a subtitle after a colon (Pressure Tested: Under the Microscope). Outside those positions, the length rule of your chosen style decides.
Real Titles That Use "Under"
- Under the Tuscan Sun by Frances Mayes. "Under" capitalized as the first word.
- Twenty Thousand Leagues Under the Sea by Jules Verne. "Under" capitalized mid-title in APA and AP; lowercase in Chicago and MLA.
- Notes from Under the Floorboards. "Under" capitalized mid-title under the 4-letter rule.
- The Country under My Skin by Gioconda Belli. Chicago style keeps "under" lowercase.
Common Mistakes
The most common error is treating "under" like a short preposition such as "on" or "to" and lowercasing it everywhere. In APA, AP, AMA, and NYT it should be capitalized mid-title because of its length. The opposite mistake is capitalizing "Under" in Chicago or MLA, where every preposition stays lowercase regardless of length. The fix for both is to pick one style guide and apply it across every title in the document rather than switching between them.
