Descriptive adverbs have three degrees of comparison. These degrees are formed in different ways.
One syllable adverbs form the comparative by adding –er. Add –est to form the superlative. Almost all the adverbs which are also used as adjectives belong to this class.
Hard, harder, hardest
Soon, sooner, soonest
Fast, faster, fastest
Late, later, latest
Adverbs which end in –ly, take more for the comparative and most for the superlative.
Sweetly; more sweetly; most sweetly
Softly, more softly, most softly
Greedily; more greedily; most greedily
Quickly; more quickly, most quickly
There is an exception to this rule.
Early, earlier, earliest
Note that a few adverbs form degrees of comparison in an irregular manner.
Well, better, best
Badly, worse, worst
Far, farther, farthest
Little, less, least
Much, more, most