Compound words can easily confuse writers. Compound nouns, for example, are variously styled closed (for example, horseshoe), hyphenated (light-year), and open (“income tax”). But correctly formatting a noun isn’t the only challenge when it comes to determining whether one word or two is appropriate. This post discusses three classes of errors in usage regarding compounds.
First, adverbs such as altogether and prepositions like nevertheless and notwithstanding are often styled “all together,” “not withstanding,” and “never the less,” but although use of these phrases is at least plausible (for example, “When they were all together, we found that they were more likely to agree”), when they serve as adverbs and prepositions, it is never correct to treat them as separate words. (Yes, all and together are both adverbs, but “all together” is a sequence of two adverbs, one intensifying the other, not a single adverb.)
On the other hand, the following phrases are never correct as one word: alot, alright, eachother, moreso, and nevermind (except, in the latter case, as the title of a certain album). (Alright is in the dictionary, and I’ve used it in this post, but those appearances are merely acknowledgments of its existence, not endorsements.) Everyday, meanwhile, is correct only as an adjective (as in the phrase “everyday savings”), not standing on its own (the correct treatment is “You’ll find savings every day”).
Then there is a large class of words that, like everyday, are correctly closed in one grammatical form and open in another. For example, when one writes that one plans to work out, the verb phrase is treated correctly. But when describing what one plans to do, one refers to “doing a workout.” This is true of numerous verb-preposition phrases such as “log in,” “break down,” and “mark up” that become closed compounds when they serve as nouns. Note, however, that there are exceptions, including come-on, in which the compound is hyphenated as shown. (Such exceptions generally persist because of the aversion to having two consecutive vowels in a compound word.)
Navigating such vagaries of the English language is annoying, but we are fortunate to have at our disposal dictionaries and other helpful resources.