In English, adverbs of manner (answering the question how?)

Adverbs - How to construct adverbs of manner.

The suffix -an/-en/-n is used to form adverbs of manner from adjectives.

Adverbs of manner:

Adverbs of manner can be formed from adjectives using the clitic 地 de (not the same character as the de used to mark possessives and relative clauses).

Adverbs of manner cannot take case suffixes - this distinguishes them from nouns that express similar meanings (as these nouns must agree in case with the nouns they modify).