feel bad vs. feel badly

Feel badly is an adverb modifying the verb, which it almost never is. In I feel badly it is linked by the verb to the subject, I, and thus it should be the adjective bad, not badly. Many well-educated people criticize the usage. It may sometimes be a hyperurbanism, resulting from fear of misusing adjectives, as He drives good, and a notion that adverbs are more elegant than adjectives.

Source: ProofreadNOW