Title Case Isn't One Rule: How AP, Chicago, and MLA Disagree on Prepositions and Hyphens

"Title Case Every Major Word" sounds simple — until you hit a four-letter preposition, a hyphenated compound, and a subtitle, and discover that AP, Chicago, and MLA style guides each have different rules for all three

Title case — capitalizing the "important" words in a title while leaving certain small words lowercase — seems like it should be a simple, universal rule. In practice, major style guides disagree on several specific cases, and even within a single style guide, the rules require knowing grammatical categories (is this word a preposition? a conjunction? how long is it?) that a simple "capitalize every word over N letters" algorithm can't reliably determine.

The basic shared principle: capitalize "major" words, lowercase "minor" words

All major style guides agree on the broad strokes:

• Always capitalize: the first and last word of the title, regardless of what part of speech it is
• Always capitalize: nouns, pronouns, verbs, adjectives, adverbs
• Generally lowercase: articles (a, an, the), coordinating conjunctions (and, but, or, nor), and (with variations, discussed below) prepositions

Where they diverge: prepositions, and which prepositions

The preposition length problem

AP Style (Associated Press): capitalize prepositions of four letters or more (e.g., capitalize With, From, Into, Over — but lowercase of, in, on, at, to, up).

Chicago Manual of Style: lowercase all prepositions, regardless of length — Into, With, From, Over would all be lowercase under Chicago style, unlike AP.

MLA Style: similar to Chicago — prepositions are lowercased regardless of length, unless the preposition is the first or last word of the title (which, per the universal rule above, is always capitalized regardless of part of speech).

A concrete example showing the divergence:

Title: "the art of war: a guide from beginners to masters"

• AP style: "The Art of War: A Guide From Beginners to Masters" — From (4 letters) capitalized, of and to (2 letters) lowercase
• Chicago/MLA style: "The Art of War: A Guide from Beginners to Masters" — from lowercase regardless of length

The same input title produces different correct outputs depending on which style guide is being followed — there is no single "correct" title case, only "correct according to a specific style guide."

Subtitles and the colon

All major style guides agree: the word immediately following a colon (starting a subtitle) is always capitalized, regardless of what part of speech it is.

"a tale of two cities: a novel" → "A Tale of Two Cities: A Novel" (with "A" capitalized as the first word of the subtitle, even though "a" as an article would normally be lowercase mid-title).

This rule is consistent across guides — but it's a rule that a simple "lowercase all articles" algorithm would get wrong, unless it specifically accounts for "is this word immediately after a colon" as an exception to the general article-lowercasing rule.

Hyphenated compounds: capitalize after the hyphen?

This is one of the most inconsistently-handled cases across style guides:

Chicago Manual of Style: generally capitalizes both elements of a hyphenated compound if both would individually be capitalized as major words — "Self-Reliance" (both "Self" and "Reliance" are capitalized). However, if the second element is a word that would normally be lowercased (an article, preposition, conjunction) — e.g., a compound like "e-mail" or certain prefix-hyphen combinations — Chicago has specific, somewhat detailed sub-rules about which second-elements get capitalized and which don't (generally: lowercase the second element if it's a suffix rather than a standalone word with its own meaning — though the exact boundary cases require consulting the specific guide's detailed examples).

AP style: generally capitalizes the first element and lowercases the second element of a hyphenated compound unless the second element is itself a proper noun or would otherwise be capitalized on its own merits — "Anti-immigrant" (lowercase "immigrant" as the second element) vs. "Pre-World War II" (capitalize "World" because it's part of a proper noun).

The practical implication for an automated tool: hyphenated compounds are the case where automated title-case conversion is most likely to need manual review — the "correct" capitalization of the second element genuinely depends on what kind of word it is (a standalone meaningful word vs. a suffix-like element) and which style guide is being followed, in ways that go beyond what a length-based or simple part-of-speech-based rule can reliably determine for all cases.

"To" as infinitive marker vs. preposition

A specific edge case: the word "to" can function as either a preposition ("give it to me") or as part of an infinitive verb form ("I want to go").

Most style guides agree "to" should be capitalized when it's part of an infinitive — e.g., "How to Win Friends and Influence People" — "to" here is part of the infinitive "to Win," and even style guides that lowercase prepositions generally still capitalize "to" in this grammatical role... though this distinction requires understanding the grammatical function of "to" in context, not just recognizing the word "to."

Why this is hard for simple algorithms: "to" appears identically whether it's a preposition or an infinitive marker — distinguishing the two requires (at least some) parsing of the surrounding sentence structure, which is a fundamentally different kind of operation than "look up this word in a list of words-to-lowercase."

Practical recommendations for automated title case

For most everyday use (not subject to a specific publication's style requirements): the AP-style "lowercase short prepositions/articles/conjunctions, capitalize everything else, always capitalize first/last words and the word after a colon" approach is a reasonable, widely-recognized default — it handles the majority of common cases sensibly, even if it doesn't perfectly replicate every style guide's every edge case.

For hyphenated compounds specifically: given the inconsistency even between major style guides, and the genuine ambiguity in some cases — treating automated title-case conversion of hyphenated words as a "first draft" requiring manual review is the most realistic expectation, rather than expecting any automated rule to be "correct" for all hyphenated compounds according to whatever specific style guide might be relevant.

If a specific style guide is required (academic writing requiring MLA/Chicago, journalism requiring AP, a specific publication's house style) — the specific guide's detailed rules (which run to multiple pages of examples and edge cases in the actual published style manuals, far beyond what's summarized here) are the authoritative reference — general-purpose title-case tools provide a useful starting point, not a guaranteed-compliant final output for contexts where strict adherence to a specific guide's every rule matters.

How to use the Case Converter on sadiqbd.com

1. Title Case conversion applies a general-purpose (AP-style-similar) ruleset — capitalizing major words, lowercasing short articles/prepositions/conjunctions, and handling first/last-word and after-colon capitalization
2. For hyphenated compounds and edge cases: review the output specifically for hyphenated words — these are the cases most likely to need manual adjustment depending on your specific style requirements
3. For strict style-guide compliance (academic papers, journalism): use the tool's output as a starting point, then cross-check against the specific style guide's detailed rules for any titles containing prepositions of borderline length, hyphenated compounds, or "to" as infinitive vs. preposition

Frequently Asked Questions

Why does my title-case tool capitalize "Of" sometimes and not other times? If a tool capitalizes "Of" as the first or last word of a title (per the universal rule that first/last words are always capitalized regardless of part of speech) but lowercases "of" in the middle of a title — this is correct behavior under the standard rules, not an inconsistency — "of" as a 2-letter preposition is lowercased mid-title under all major style guides, but the first/last word exception applies regardless of what the word is.

Is there a "correct" title case for non-English titles? Title case capitalization conventions are largely an English-language convention — many other languages have different conventions for title/heading capitalization (some capitalize only the first word and proper nouns, regardless of "major/minor" word status — closer to what English calls "sentence case") — applying English title-case rules to non-English text generally isn't appropriate; the relevant convention is whatever that language's own typographic/editorial conventions specify, which can differ substantially from English title case.

Is the Case Converter free? Yes — completely free, no sign-up required.

Try the Case Converter free at sadiqbd.com — convert text to title case, sentence case, camelCase, and more instantly.