Making good grammar decisions usually requires very little grammar. If the sentence "Whom are you?" sounds wrong, it probably is. You don't need to know why. You need never have heard the term "predicate nominative" or even "object pronoun." Call it grammar autopilot.
But there are exceptions — specifics and subtleties of the language that require extensive grammar for a small payoff. The most striking example is "a while" and "awhile." To know which one to use, you need to know what a preposition is, you need to know what the object of a preposition is, you need to know what an adverbial is, and you need to know what an adverb is. That last one is harder than you may realize.
Most people would define an adverb as a word that usually ends in "ly" and describes the action in a verb, like "quickly" in "Brian ran quickly" or "happily" in "Harper sang happily." But that's not the definition of an adverb — it's just one type, called a "manner adverb" because it describes the manner in which an action took place.
Adverbs are a broader category that includes "there," as in "Put it there," and even "tomorrow," as in "I'll see you tomorrow." The best definition of an adverb is a word that indicates manner, time, place or degree.
So because the "there" in "Put it there" indicates place, it's an adverb in this sentence. Because "tomorrow" in "I'll see you tomorrow" indicates time, here it's an adverb.
The word "awhile" also indicates time — specifically, a duration. So it's an adverb. But "a while" is not an adverb. It's a noun phrase, made up of the noun "while" and an article. (Like many words, "while" isn't limited to one part of speech. It's often a conjunction too. But in "a while" it's always a noun.)
Here's where things get tricky. Adverbs aren't the only terms that can function adverbially. Compare the sentences "I'll see you tomorrow" and "I'll see you Tuesday." The words "tomorrow" and "Tuesday" perform identical jobs. They're both functioning as adverbials, answering the question "when?" But according to Merriam-Webster's Collegiate Dictionary, "tomorrow" is an adverb but "Tuesday" is a noun.
Why? Because word classes like "adverb," "noun" and "verb" are like clubs. They're labels we give to words that commonly perform certain jobs. When lexicographers see that a word is regularly used adverbially, they label it an adverb. When the word only occasionally works adverbially, it doesn't merit membership in the adverb club. But it can still have an adverbial function in a sentence.
Why does this matter? Because when you say "Stay awhile," you're using an adverb as the adverbial. But when you say "Stay a while," you're using a noun phrase as an adverbial. And both are correct.
Yet "awhile" and "a while" aren't always interchangeable. There's one situation where "awhile" won't do. But to understand it, you need to understand prepositions.
Prepositions like "for" take objects, which are noun phrases (nouns or pronouns with or without articles or other modifiers). So when you add the preposition "for" to our example sentence, only a noun phrase can follow: Stay for a while. The one-word "awhile" can't function as the object of the preposition because it's an adverb.
So the noun phrase "a while" can function either as the object of a preposition or as an adverbial. But the adverb "awhile" can function only as an adverbial. That's why "Stay for awhile" is always wrong, even though "Stay awhile" is right.
If you want a simple way to navigate this mess — a way that doesn't require advanced grammar — always use the two-word "a while." I suppose I could have told you so 500 words ago. But this way, at least, I got you to stay awhile.
JUNE CASAGRANDE is the author of "It Was the Best of Sentences, It Was the Worst of Sentences." She can be reached at JuneTCN@aol.com.