The difference is shown in the following pair of sentences. This apple smells sweet . Your dog smells carefully . Saying you feel badly is like saying you feel gladly . Good is an adjective, so you do not do good or live good , but you do well and live well .
Confusion can occur because well can function either as an adverb or an adjective.
Double-negatives Scarcely and hardly are already negative adverbs. To add another negative term is redundant. They found scarcely any animals on the island. Hardly anyone came to the party. Sure is an adjective, and surely is an adverb.