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AP vs Chicago (CMOS) Title Case Rules Comparison

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Sam Brown

Sam is an editor, ghostwriter and 7x Top Writer on

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Associated Press (AP) Stylebook and Chicago Manual of Style (CMOS) are two of the most widely used guides for Title Case formatting rules. Chicago has its roots in academia whereas AP is focused on journalism.

Whilst they agree on several points, there are some key differences that you should be aware of.

Let’s dive into the similarities and differences between AP and Chicago Title Case rules. Finally, we’ll discuss what rules we chose for TitleFormat and why.

AP Vs CMOS: What They Agree On

Associated Press Stylebook and Chicago Manual of Style both agree on the following:

  • Capitalize the first word.
  • Capitalize the last word.
  • Capitalize all verbs, nouns, pronouns, and adjectives.
  • Do not capitalize articles and prepositions of 3 letters or fewer.
  • Do not capitalize conjunctions for, and, nor, but, or.

AP Vs CMOS: How They Differ

In AP, the conjunctions yet and so are lowercased, as with all other conjunctions, however in Chicago style, these two conjunctions are capitalized.

In CMOS, as is always lowercase whereas in AP, it is capitalized when used as an adverb.

In AP style, prepositions of 4 letters or more are capitalized, whereas in CMOS, all prepositions are lowercase. This particularly affects from, into, unto, and with which are lowercase in CMOS but capitalized in AP.

In AP style, to in infinitives is capitalized, whereas in CMOS it is lowercase.

A final peculiarity is that AP prescribes Sentence Case for headlines and only specifies Title Case for titles of works (books, movies, songs etc). In practice, many writers use AP title capitalization rules for headlines and article titles.

AP Vs CMOS Differences Table

This table highlights some of the key differences between AP and Chicago Title Case rules.

as (adverb) Lowercase Capitalized
as (conjunction) Lowercase Lowercase
if Lowercase Capitalized
so Lowercase Capitalized
to (in infinitives) Capitalized Lowercase
yet Lowercase Capitalized
from Capitalized Lowercase
into Capitalized Lowercase
unto Capitalized Lowercase
with Capitalized Lowercase

Which Rules Does TitleFormat Follow?

TitleFormat does not follow any one set of rules. Instead, based on our many years experience writing online, we have cherrypicked the rules that make the most sense in most situations.

Chicago Manual of Style rules are highly prescriptive and, frankly, confusing. Not only to the headline writer but they can also appear inconsistent to the reader. For example, the word like would be capitalized when used as an adjective, conjunction, noun, or verb but lowercased when used as a preposition.

AP rules are more consistent and TitleFormat is more closely aligned with these however, unlike AP, TitleFormat always lowercases as and to for consistency and simplicity.

TitleFormat applies the following rules:

  • Capitalize the first word
  • Capitalize the last word
  • Capitalize any words of 4 letters or more
  • Do not capitalize articles (a, an, the…)
  • Do not capitalize coordinating conjunctions (and, but, for…)
  • Do not capitalize short prepositions (at, by, to, on…)
  • Do not capitalize to in infinitives
  • Capitalize the first part of a hyphenated word and subsequent parts, unless the word should be lowercased as per any of the above rules. eg “Case-by-Case”

Try it now.

Tags: Title case basics

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