cooperate: Style Guide Spelling Decisions (AP, Chicago, MLA, APA)

How major style guides rule on "cooperate"

All American guides close the compound; British editors sometimes retain 'co-operate' but the closed form is standard.

The disagreement on "cooperate" is an example of hyphenation rules for common prefixes, 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.

What the divergence actually means

Unlike many compound-modernization decisions where style guides eventually converge, "cooperate" 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 "cooperate", 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 "cooperate", 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

Garner's Modern English Usage classifies the "cooperate" / "co-operate" pair on its Language-Change Index, a five-stage scale measuring whether a once-disputed form has been accepted into Standard English. For hyphenation rules for common prefixes, Garner's typically rates the dominant form at Stage 4 ("ubiquitous but objected to by traditionalists") or Stage 5 ("fully accepted"). Source: Garner's Modern English Usage, 5th Edition

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 "cooperate" reflect not disagreement about correctness but different audiences and editorial pressures.

Editorial context

Google Books N-grams data for American English show the closed spelling cooperate surpassing the hyphenated co-operate around 1830, with the unhyphenated form achieving near-total dominance by the 1920s as dictionary makers like Funk & Wagnalls and newspaper stylebooks standardized it amid the rise of Linotype machines that favored solid compounds for faster composition. This corpus crossover predates major twentieth-century guides, highlighting how publishing practicality, avoiding fragile hyphens in prefixes like co-, re-, and pre-, drove the shift rather than prescriptive fiat. In British English, the turnover lagged, occurring around 1980, which accounts for lingering hyphenation in conservative outlets. Consider Local authorities urged residents to co-operate with emergency services., a phrasing still attested in UK print media despite the closed form's statistical lead in recent decades.

Cross-references

For the dictionary entry, frequency data, and pronunciation of cooperate, see the main word page. For other style-guide spelling decisions in this category, browse all style-guide spelling rulings.