AP, Chicago, MLA, and APA Title Case Rules Explained Simply
Every editor has a moment of genuine panic when they realize they've been capitalizing titles wrong for years. Maybe you've been lowercasing "is" in every headline you've written, then someone points out that AP style capitalizes it. Or you've been writing "Into the Wild" when your publication actually wants "Into The Wild." These aren't trivial quibbles. If you submit work to a publication or academic journal with the wrong style, it signals that you either didn't read the guidelines or don't take the details seriously. Neither impression is good.
The four dominant style guides — AP, Chicago, MLA, and APA — each have their own logic for title case, and each has quirks that trip people up. This guide cuts through the noise and explains what each system actually requires, including the genuinely confusing edge cases around small words.
Why Title Case Isn't Universal
Before diving into each system, it helps to understand why they differ at all. These style guides evolved in different professional contexts with different audiences. AP emerged from newspaper journalism, where clarity and space efficiency matter. Chicago developed for book publishing and academic presses, where exhaustive precision is the norm. MLA is shaped by literary scholarship. APA comes from social and behavioral sciences, where standardization across research papers drives every decision.
Each community developed slightly different conventions, and those conventions calcified into rules. The result is four overlapping but not identical systems that professionals genuinely need to navigate depending on where they're publishing.
AP Style: The Journalist's Title Case
The Associated Press Stylebook is the standard for newspapers, magazines, and a lot of web content. Its title case rules are fairly intuitive, which is probably why AP is often the default people learn first.
In AP style, you capitalize the first and last words of a title regardless of what they are. Between those anchor points, capitalize all "principal words" — which AP defines as nouns, pronouns, adjectives, verbs, adverbs, and subordinating conjunctions. The words you leave lowercase are articles (a, an, the), coordinating conjunctions (and, but, for, nor, or, so, yet), and prepositions of any length.
That last part is worth pausing on. AP lowercases prepositions regardless of length. So "into," "between," "through," "underneath" — all lowercase unless they're the first or last word. This puts AP somewhat at odds with Chicago on the preposition question.
Where AP gets tricky: "to" as an infinitive marker is lowercased (AP treats it like a preposition for this purpose), but verbs in their full form get capitalized. So "How to Win Friends" would lowercase "to" but capitalize "Win." Another stumper: "is," "are," "was," "were," and other forms of "to be" — these are verbs and get capitalized in AP. Always. That's where writers make the most mistakes.
AP example: The Man Who Sold the World: A History of Rock in the 1970s
Chicago Style: The Publisher's Title Case
The Chicago Manual of Style is the most detailed of the four guides and the one most commonly used in book publishing and longform journalism. Its title case rules are similar to AP in spirit but differ on a few meaningful points.
Chicago capitalizes the first and last words of a title, plus all "major words." Major words include nouns, pronouns, verbs, adjectives, adverbs, and subordinating conjunctions. So far, identical to AP. The difference is in how Chicago handles prepositions.
Chicago lowercases "short" prepositions — specifically, those with four letters or fewer. So "at," "by," "for," "in," "of," "off," "on," "out," "per," "to," "up," and "via" all get lowercased. But "above," "after," "along," "among," "around," "before," "between," "beyond," "down," "from," "into," "near," "onto," "over," "past," "than," "through," "under," "until," "upon," "with," and "within" — five letters or more — get capitalized in Chicago style.
That's a genuine difference from AP. "Into" is lowercase in AP; it's capitalized in Chicago.
Chicago also lowercases "to" when it's used as part of an infinitive, same as AP. Coordinating conjunctions (for, and, nor, but, or, yet, so — the FANBOYS list) are lowercased unless they appear at the start or end. Articles are lowercased. The word "as" gets lowercased when it's a conjunction or preposition, but capitalized when it functions as an adverb.
One Chicago-specific detail that surprises people: hyphenated compounds. Chicago capitalizes both elements of a hyphenated word in a title if they're both major words ("Self-Reliance," "Well-Being") but not necessarily if the second element is a modifier that wouldn't normally be capitalized on its own.
Chicago example: The Man Who Sold the World: A History of Rock in the 1970s
Same headline, different treatment of "Into" if it appeared: Chicago would capitalize it, AP wouldn't.
MLA Style: The Academic Humanist's Title Case
MLA style, from the Modern Language Association, is primarily used in humanities scholarship — literature, languages, film, cultural studies. Its title case system is actually quite close to Chicago, which makes sense given their shared roots in academic publishing.
MLA capitalizes the first word of a title, the first word of a subtitle, and all "principal words." It lowercases articles, prepositions, coordinating conjunctions, and the infinitive marker "to." What counts as a preposition is handled similarly to Chicago, though MLA's guidance tends to be less granular about the exact length threshold — most MLA guides in practice align with the four-letter rule.
Where MLA diverges from Chicago in ways that matter: MLA is slightly more permissive about context. If a preposition is part of a phrasal verb — "look up," "give in," "set off" — MLA capitalizes the particle even though it looks like a preposition. So "Looking Up Answers" would capitalize "Up" because it's part of the verb phrase, not a pure preposition. AP and Chicago take the same general position here, but MLA's style manuals spell it out clearly.
For works cited entries, MLA uses title case for book titles and article titles consistently. This distinguishes it from APA, where the rules change depending on what you're citing.
MLA example: Looking Up the Answers: A Study of Research Methods in Literature
APA Style: The Social Scientist's Title Case
APA style, from the American Psychological Association, is used across psychology, sociology, education, and the social sciences. Its title case rules are the most context-dependent of the four, and that's where the real confusion starts.
In APA, whether you use title case depends entirely on where the title appears:
- In running text (when referring to a work within your prose): Use title case.
- In the reference list (bibliography): Use sentence case for journal articles and book chapters — only the first word, the first word after a colon, and proper nouns get capitalized.
- Journal names in the reference list: Always title case, regardless.
This dual system is genuinely unusual and catches people off guard. You might write "I analyzed the findings from The Social Construction of Reality" in your text (title case), then cite it in your references as "The social construction of reality" (sentence case). Both are correct APA — they're just in different locations.
When APA does use title case, the rules align with Chicago and MLA: capitalize major words, lowercase articles and short prepositions and coordinating conjunctions. The seventh edition of the APA Publication Manual also explicitly capitalizes the first word after a colon in a subtitle, even in sentence case contexts.
APA in-text reference: The Social Construction of Reality (title case)
APA reference list: The social construction of reality (sentence case)
The Small Words That Break Every System
Across all four styles, certain words cause consistent confusion because their grammatical role changes depending on context.
"As" is the canonical example. As a conjunction ("She sang as the sun set") or preposition ("She works as a consultant"), it's lowercased. As an adverb meaning "equally" or "to the same degree," Chicago capitalizes it. Most editors throw up their hands and just lowercase it everywhere, which is technically only right sometimes.
"If" is a subordinating conjunction — all four style guides capitalize it, though many writers lowercase it because it feels like a small word. The rule is about grammatical function, not character count.
"So" as a coordinating conjunction (FANBOYS) is lowercased. As an adverb ("The work was so thorough"), it would be capitalized. In practice, context usually makes this obvious.
"Yet" follows the same split: coordinating conjunction gets lowercased, adverb gets capitalized.
A Practical Decision Framework
If you're writing for a specific publication, read their style guide and use a tool to double-check your titles. Most content management systems and editorial tools can apply a chosen style automatically, though they frequently get the edge cases wrong — especially hyphenated compounds and context-dependent words like "as."
If you're working academically, check your institution's or journal's requirements first. Many explicitly specify which style they follow, and they mean the whole style guide, not just the title capitalization rules.
The underlying principle across all four systems is the same: major words carry meaning and deserve visual prominence; function words (prepositions, articles, conjunctions) serve grammatical structure and stay lowercase. Once you internalize that logic, the specific rules become variations on a theme rather than arbitrary rules to memorize.
The tricky cases will still trip you up occasionally. That's not a failure — it means the grammar is doing something genuinely interesting. When you're unsure about a specific word, ask what role it's playing in the sentence. Is "over" introducing a prepositional phrase, or is it part of a phrasal verb like "get over"? The answer to that question is the answer to whether you capitalize it.
Style guides exist to create consistency within a community of writers and readers. Learn the system your community uses, internalize the logic behind it, and keep a reference handy for the edge cases. The specifics vary; the underlying respect for clear, consistent presentation doesn't.