Title Case Rules: APA, AP, Chicago and MLA Compared

Why there is more than one set of rules

There is no single law of capitalization for titles. Each style guide was written for a different audience: AP for news, APA for the social sciences, Chicago for books and the humanities, MLA for literature and language studies. They agree on the basics, but they draw the line between big and small words in different places.

The result is a few predictable differences. They concern the length of prepositions, the treatment of conjunctions such as as and than, hyphenated words and what happens after a colon. If you know where the differences are, you can adjust the output of any converter in seconds. The converter on this page offers APA/AP, Chicago and MLA as separate options for this reason.

What all four styles agree on

All four capitalize the first and the last word of a title, whatever they are. All capitalize nouns, pronouns, verbs, adjectives and adverbs, including short verbs such as is, be and are. All lowercase the articles a, an and the, unless the article is the first word. And all lowercase the coordinating conjunctions and, but, for, nor and or in the middle of a title.

The AP Stylebook states its rule for the titles of works shortly: capitalize the principal words, capitalize prepositions and conjunctions of four or more letters, lowercase the articles the, a and an, and capitalize the first and last words, which overrides the other rules. Everything beyond these basics is where the guides part ways.

APA: four letters or more

APA, in its 7th edition, capitalizes all words of four letters or more. That includes prepositions such as with, from, into and over, and conjunctions such as that or than when they are long enough. The shorter minor words stay lowercase: articles, conjunctions and prepositions of three letters or fewer, such as and, in, of, on, at and by.

The first word of the title and the first word of a subtitle after a colon are capitalized. Major words are capitalized wherever they appear, including the second word of a hyphenated major word, so the standard form is Self-Report, not Self-report. The second word after a prefix in a compound modifier, such as Mid-year, can remain lowercase. APA uses title case for titles in the text but sentence case for the titles of articles and books in the reference list.

AP: prepositions and conjunctions of four letters or more

For the titles of books, films, songs and other works, the AP Stylebook capitalizes the principal words and prepositions and conjunctions of four or more letters. Articles stay lowercase, and so do the shorter prepositions and conjunctions. The practical results are almost the same as APA: with, from, over and between are capitalized, and in, of and on are not.

AP also capitalizes the first and last words of the title. Published summaries of the 2020 edition say that AP capitalizes the word to in infinitives, which most other styles do not; the Stylebook itself is the final authority on this point, and the converter on this page lowercases to in every style. For news headlines, the AP Stylebook uses a different approach: it asks for sentence-style capitalization, with a capital only on the first word and on proper nouns. The four-letter rule is therefore the AP rule for titles of works, not for the headlines of news stories.

Chicago: the 18th edition changed the rule

The Chicago Manual of Style has the longest history of the four. In older editions, Chicago lowercased articles, coordinating conjunctions and prepositions regardless of length. So with, between and through were all lowercase. The Chicago Manual's own question-and-answer page records this as the traditional rule, adding that prepositions stay lowercase except as the first or last word of a title.

The 18th edition, published in 2024, changed this: prepositions of more than four letters are now capitalized in titles. Prepositions of four letters or fewer, such as with, from, into and over, stay lowercase, while between, through and about are capitalized. The word as is lowercase in Chicago, and so is to. Since the 17th edition, the second word after a hyphenated prefix is capitalized, as in Mid-Year or Anti-Hero. Chicago lowercases the same articles and coordinating conjunctions as the other styles.

MLA: lowercase all prepositions

MLA has the simplest rule for prepositions: do not capitalize prepositions of any length. Articles, coordinating conjunctions and prepositions stay lowercase unless they are the first or last word. In MLA, "A Walk between the Trees" is correct, and "Through the Looking-Glass" starts with a capital letter only because it is the first word.

Subordinating conjunctions such as if, because, although, while and that are capitalized, and so are the words that complete a phrasal verb, as in Set Up and Log In. The first word of a subtitle is capitalized. The second part of a hyphenated major word is capitalized in the title, so MLA writes Self-Report, while compound modifiers after a prefix such as Mid-year may stay lowercase.

Which style to choose and how to apply it

The choice is rarely yours: an instructor, a journal or an employer names the style. If no one does, choose one and apply it throughout. APA/AP is a sensible default for headlines and articles because its rule is easy to remember and easy to apply: capitalize everything of four letters or more.

In the converter, choose the style from the Title case style menu and click Title Case. The text is lowercased first, then capitalized according to your style, and the first word, the last word and the first word after a colon are always capitalized. Check proper nouns, brand names, acronyms and phrasal verbs by hand, because no automatic tool can know them. The rules above come from the guides themselves and from summaries by editors; if your publisher sends its own list, the publisher's list wins.