A while and awhile have different meanings. A while is a noun phrase and means “a period of time.” In contrast, awhile is an adverb, and it means “for a time.” This may seem confusing, so keep reading for several helpful examples and tricks.
In a previous Grammar Girl post, I talked about using while to mean although, but another point about while can confound people: What is the difference between a while and awhile?
A while describes a time, a noun. The article a before while is a sure sign that you're dealing with a noun. Notice in the following sentence that you could replace a while with another article-noun combination such as a year:
It's been a while since Squiggly tried marmite.
It’s been a year since Squiggly tried marmite.
Both of those sentences describe a length of time: a while is more general and a year is more specific, but they’re both a length of time. (Actually, when you use a year like that, it’s usually also at least somewhat general because it probably hasn’t been exactly a year since Squiggly tried marmite.)
Awhile means "for a time,” and it's an adverb. Notice in the following sentence that you could replace awhile with another adverb such as quietly:
Go play awhile.
Go play quietly.
Finally, just to make it confusing, if you rephrase Go play awhile and replace the adverb with a prepositional phrase, you need the noun again because an adverb can't be the object of the preposition.
Go play awhile. (The adverb is modifying the verb.)
Go play for a while. (The article and noun are the object of the preposition.)
The Quick and Dirty Tip is that awhile and a while both describe a vague length of time, but you use the one-word version when you need an adverb and the two-word version when you need a noun.
To tell the difference, you can test your sentence with other nouns and adverbs. If you can replace a while with another article and noun such as an hour or a year, you know you want the two-word version. If you can replace awhile with another adverb such as quietly, longer, or briefly, you know you want the one-word version.
NOTE: As is so often the case, English usage isn’t simple. Most sources I checked (Chicago, Garner, AP Stylebook) recommend the guidelines I give in this article, but I found one dissenter: an American Heritage Dictionary usage note says that the noun phrase a while can be used adverbially, so that both Go play awhile and Go play a while are correct. I’m sticking with my advice, but I thought you should know that although it is the most common advice and the safest choice, it’s not universal.
Also, Garner and the Merriam-Webster online dictionary note that the use of awhile as the object of a preposition (Go play for awhile) is increasing. It is still most often called an error, however, and Garner calls it a “stage 1” error in his ranking system, which means it is the least acceptable kind of error.
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