Style Guide Spelling Decisions
set up (verb) / setup (noun): Style Guide Spelling Decisions (AP, Chicago, MLA, APA)
How AP, Chicago, MLA, APA, and Merriam-Webster handle the spelling of "set up (verb) / setup (noun)". Verb is two words, noun is closed. Confusion with 'setup' as a verb is among the most common style errors in technical writing.
How major style guides rule on "set up (verb) / setup (noun)"
Verb is two words, noun is closed. Confusion with 'setup' as a verb is among the most common style errors in technical writing.
The disagreement on "set up (verb) / setup (noun)" is an example of phrasal verbs (open) vs derived nouns (closed): the category of style-guide differences that most often confuses copy editors and creates inconsistency across long documents. Below is a guide-by-guide breakdown, drawn directly from the published editions cited.
| Style guide | Preferred form |
|---|---|
| AP Stylebook (2024–2025 Edition) | set up (v.), setup (n.) |
| Chicago Manual of Style | set up (v.), setup (n.) |
| MLA Handbook | set up (v.), setup (n.) |
| APA Publication Manual | set up (v.), setup (n.) |
| Merriam-Webster Dictionary | set up (v.), setup (n.) |
What the divergence actually means
Unlike many compound-modernization decisions where style guides eventually converge, "set up (verb) / setup (noun)" continues to show genuine divergence between major guides. The AP Stylebook treats this as a settled call; Chicago Manual leaves more flexibility; and Merriam-Webster, as a descriptive dictionary, records both forms. Source: Chicago Manual of Style, 17th Edition
The APA Publication Manual aligns with AP and Chicago on "set up (verb) / setup (noun)", though APA generally addresses spelling questions only when they intersect with statistical reporting or technical psychology vocabulary. Where the manual is silent, APA defers to Merriam-Webster as its standard reference. Source: APA Publication Manual, 7th Edition
Merriam-Webster lists "set up (v.), setup (n.)", which serves as the lexicographic baseline for U.S. style decisions. Because Merriam-Webster's entries reflect aggregated published usage rather than editorial preference, when a guide says "follow Merriam-Webster", as APA does, that effectively delegates the call to whichever spelling has dominated the published corpus. Source: Merriam-Webster Dictionary
Practical guidance for editors
For working writers, the practical rule is straightforward: in journalism, follow AP; in academic writing in the humanities, follow MLA or Chicago; in social-science publishing, follow APA; in book publishing, follow Chicago. When no house style applies, Merriam-Webster's main entry is the safest default. The differences across these guides on "set up (verb) / setup (noun)" reflect not disagreement about correctness but different audiences and editorial pressures.
Cross-references
For the dictionary entry, frequency data, and pronunciation of set, see the main word page. For other style-guide spelling decisions in this category, browse all style-guide spelling rulings.