log in (verb) / login (noun): Style Guide Spelling Decisions (AP, Chicago, MLA, APA)

How major style guides rule on "log in (verb) / login (noun)"

Universal: the verb is two words ('log in to your account'), the noun is one word ('your login').

The disagreement on "log in (verb) / login (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.

What the divergence actually means

Unlike many compound-modernization decisions where style guides eventually converge, "log in (verb) / login (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 "log in (verb) / login (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 "log in (v.), login (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

Garner's Modern English Usage classifies the "log in (v.) / login (n.)" / "login (verb)" pair on its Language-Change Index, a five-stage scale measuring whether a once-disputed form has been accepted into Standard English. For phrasal verbs (open) vs derived nouns (closed), 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 "log in (verb) / login (noun)" reflect not disagreement about correctness but different audiences and editorial pressures.

Editorial context

In computing's foundational documentation, such as the original 1970s Unix manual pages, login functions as a one-word verb for the command initiating user sessions, a convention that persists in technical writing, command-line interfaces, and developer forums despite formal style distinctions. This industry-specific usage, rooted in early systems like Multics (1960s) and carried forward in Linux distributions, prioritizes compactness and tradition over phrasal separation; for example, programmers routinely instruct *login as root* or label buttons Login in application code. Even as general English adopted "log in" for the verb by the 1990s, evidenced in OED citations from 1983 onward, the alternative endures in open-source repositories like GitHub, where "login" appears millions of times in README files and scripts. Copy editors bridging tech and mainstream publishing thus encounter persistent resistance, as software APIs and error messages reinforce the fused form, complicating adherence to noun-verb splits in hybrid contexts.

Cross-references

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