Quick Answer
The Two Roles of "In": Preposition vs. Adverb
"In" is one of the most versatile words in English. Most of the time, it's a preposition – a word that shows a relationship between a noun and another element. "In the morning," "in the kitchen," "in the novel" – all prepositions. When "in" is a preposition, capitalization is straightforward: all four guides lowercase it because it's a short function word.
But "in" also appears in phrasal verbs – two-word verbs where a preposition or adverb changes the meaning of the base verb. "Sign up," "check out," "log in," "drop by" – the second word is technically an adverb, not a preposition, even though it looks identical. This is where guides diverge.
The distinction matters because guides have different philosophies about phrasal verbs. Some argue that phrasal verbs function as single units and should follow capitalization rules for verbs (capitalize them). Others treat the individual words and apply standard preposition rules (lowercase them). This philosophical difference creates the only real controversy about "in" in title case.
By Style Guide
| Style Guide | “in” in middle of title? | Rule |
|---|---|---|
| AP | Lowercase | Lowercase as preposition (3 letters); capitalize as adverb in phrasal verbs |
| APA | Lowercase | Words under 4 letters stay lowercase, including in phrasal verbs |
| Chicago | Lowercase | Lowercase as preposition (3 letters); capitalize as adverb in phrasal verbs |
| MLA | Lowercase | Words under 4 letters stay lowercase, including in phrasal verbs |
The key to understanding when guides differ is recognizing phrasal verbs. A phrasal verb is a verb plus a preposition or adverb that together form a new meaning. "Look up" means research, not gaze upward. "Log in" means access a system, not physically enter. In titles, AP and Chicago capitalize "in" when it's part of a phrasal verb ("Sign In to Your Account"), while APA and MLA always lowercase it ("Sign in to Your Account"). Both approaches are defensible – they reflect different philosophies about how to handle function words in compound verbs. Choose your guide and stay consistent.
Examples
✓ Do
- Information in the Database
- Managing Inventory in Your Store
- Finding Facts in the Archives
- Working in the Cloud
✗ Do not
Information IN the Database
Random capitalization — never correct
in the database
No title case applied at all
AP/Chicago (phrasal verb — also correct)
- Sign In to Your Account
- Log In to Your Email
- Check In Anytime
APA/MLA (phrasal verb — also correct)
- Sign in to Your Account
- Log in to Your Email
Edge Cases
A few situations where the standard rules shift:
- Phrasal verbs in titles: the contested territory. Common phrasal verbs with "in" include: sign in, log in, check in, fill in, move in, dive in, tune in. The solution: pick your guide and document it. AP/Chicago capitalize "In"; APA/MLA keep it lowercase.
- "In" as the first word of a title. Every style guide agrees: capitalize the first word of a title. "In the Beginning" capitalizes "In" regardless of which style guide you follow.
- "In" as the last word of a title. All four guides require capitalizing the last word. If your title ends in "in," capitalize it. This overrides all other rules.
- "In" after a colon or dash. Treat text after a colon as a new title segment. If "in" starts this segment, capitalize it. "How to Build an App: In 30 Days or Less" — capitalize "In."
Frequently Asked Questions
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About Oleh Kovalenko
Oleh Kovalenko develops practical capitalization guidance for editorial and SEO workflows, with a focus on consistent rule application.
