Some words ending in –ly are adjectives, and not normally adverbs. Examples are: costly, cowardly, deadly, friendly, likely, lively, lonely, silly, miserly and unlikely.
Incorrect: He behaved cowardly.
Correct: He behaved in a cowardly manner.
Correct: He behaved like a coward.
Correct: He behaved in a cowardly manner.
Correct: He behaved like a coward.
Incorrect: He laughed silly.
Correct: He gave a silly laugh.
Correct: He gave a silly laugh.
Incorrect: He lives miserly.
Correct: He lives in a miserly way.
Correct: He lives in a miserly way.
In the sentences given above the words cowardly, silly and miserly are all adjectives which cannot be used to modify verbs. And because there are no adverbs for these meanings we have to use adverb phrases like ‘in a cowardly manner’ and ‘in a miserly way’ to express the same idea.
