remarkably diligent" and "He works very faithfully," the adverbs modify
the adjective _diligent_ and the other adverb _faithfully_ by expressing
the degree of diligence and faithfulness.

Adverbs are chiefly used to express in one word what would otherwise
require two or more words; thus, _There_ signifies in that place;
_whence_, from what place; _usefully_, in a useful manner.

Adverbs, like adjectives, are sometimes varied in their terminations to
express comparison and different degrees of quality.

Some adverbs form the comparative and superlative by adding _er_ and
_est_; as, _soon_, _sooner_, _soonest_.

Adverbs which end in _ly_ are compared by prefixing _more_ and _most_;
as, _nobly_, _more nobly_, _most nobly_.

A few adverbs are irregular in the formation of the comparative and
superlative; as, _well_, _better_, _best_.


PREPOSITION

A _preposition_ connects words, clauses, and sentences together and shows
the relation between them. "My hand is on the table" shows relation
between hand and table.

Prepositions are so called because they are generally placed _before_ the
words whose connection or relation with other words they point out.