Real is an adjective that means “not imaginary or fake or artificial.” It is used before a noun to describe it.
Real cheese (not artificial cheese)
Real Gucci bag (not a fake or knock-off)
Real numbers (not imaginary numbers, e.g., 6i)
Really is an adverb that means “actually or truly or very.” It is used to modify a verb or
adjective or another adverb (not a noun).
I’m really working. (modifies verb)
I’m really hungry. (modifies adjective)
I’m eating really quickly. (modifies adverb)
Which brings us to Wrangler’s trademarked advertising slogan:
Real. Comfortable. Jeans.
Now, if these pants are not imaginary or fake, then “real” would be correct. However, if “real” is actually describing how comfortable these pants are, that would be an adverb modifying an adjective, and “really” would be correct.
Don’t even get me started on the grammatical incorrectness of one-word sentences with no verb – and even no subject!
It seems to be a fad in advertising these days to use three one-word sentences in a row as a slogan or tagline.
Sony has one: “like.no.other.”
Piedmont Virginia Community College has one, too: “Opportunity. Access. Excellence.”
If I see another new one: I’m. Gonna. Barf.