last changed in 2002
`Adverb' is the name of one of the main word-classes, but it is undoubtedly the least convincing word-class because it has so few distinctive characteristics. Here is a list of distinctive characteristics that are shared by words which are clear adverb:
QUICKLY, EXTREMELY, SUFFICIENTLY; BADLY, WELL.
(1) They (have) frequently/often walked to work.
(2) They acted quickly/*quick.
(3) Their quick/*quickly action saved the day.
(4) extremely/*extreme quick/quickly
In general, if a word can be replaced by an ly-adverb (i.e. an adverb such as QUICKLY or EXTREMELY derived from an adjective), it is probably an adverb; putting it another way, if a word can be replaced by an ly-adverb, it must be being used in a way which is permitted for adverbs, so you can safely call it an adverb unless you have good reasons for thinking otherwise. (For example, this morning can often be replaced by recently, but we have excellent reasons for believing that both this and morning are nouns.)
See also: sentence adverb.
This is an article from the Encyclopedia of Word Grammar and English grammar. If you refer to it, please give the url as "http://tinyurl.com/wg-encyc".