Take, for example, one student's recent lament that people shouldn't use "real" in place of "really" in a sentence like "Pete works real hard."
On the surface, her complaint makes sense: Adverbs like "really" modify adjectives like "hard." There's no doubt that "Pete works really hard" is correct. And it sounds nice and proper, too.
You could say that the "real" in "Pete works real hard" is substandard. You could say it's improper. You could say it's dialectical, low rent, nonstandard or even icky. But you can't say it's wrong.
A simple check of the dictionary proves this: "Webster's New World College Dictionary" and "Merriam-Webster's" online dictionary both list "real" as an adverb meaning "very." So "Pete works real hard" is grammatical, according to these dictionaries.
Though "real" can pinch hit for "very," it's not as versatile as "really." Sure, "real," like "very," can modify adjectives, as in "She's real smart." But "real" can't modify verbs, as in "She real is suffering." For that, only "really" will do: "She really is suffering."
That's what I told my students. But then, in one of those moments of cosmic justice, a student put me on the spot: Why, she asked, if "real" is acceptable as an adverb, is it so widely considered improper?
"Whys" aren't really my strong suit. I'm more a "whether" person, focusing on whether you can use certain words certain ways. So to answer her question, I had to dig a little deeper.
I started with "Fowler's Modern English Usage," which taught me that using "real" to mean "very" is mainly an American and Scottish thing. Brits aren't as prone to this "informal" usage.
"Garner's Modern American Usage" notes that "real" can function as an adverb but calls it "dialectical."