289. Most monosyllabic adverbs add -er and -est to form the comparative and superlative, just as adjectives do; as, high, higher, highest; soon, sooner, soonest.
Adverbs in -ly usually have more and most instead of the inflected form, only occasionally having -er and -est.
Its strings boldlier swept.—Coleridge.
None can deem harshlier of me than I deem.—Byron.
Only that we may wiselier see.—Emerson.
Then must she keep it safelier.—Tennyson.
I should freelier rejoice in that absence.—Shakespeare.
Form vs. use.
290. The fact that a word ends in -ly does not make it an adverb. Many adjectives have the same ending, and must be distinguished by their use in the sentence.