Every Day vs. EverydayHow to use "every day" and "everyday" correctly
There are a number of expressions in English that can be written both as a single word and as separate words, each with a distinct usage or part of speech. The most problematic of these are “every day” and “everyday.” As a compound word, everyday should only be used as an adjective to describe ordinary things that are used or encountered frequently:
For an adverbial description, write the words separately:
go to the office every day
In the sentence above, “every day” does not modify a noun; it is an adverb because it tells when someone goes.
It might help to remember this distinction by thinking of the hit song “Everyday People,” originally performed by Sly and the Family Stone.
Common Errors in English Usage: Errors in diction and idiom commonly made by native speakers of English
List of Common Errors in English Usage (PDF): Printable version of the complete list
Common Grammar Errors: A list of common errors in grammar (topics like subject-verb agreement and parallelism) as distinct from usage