Comparatives are the forms of an adjective or adverb which are used to compare the quality of two or more things. There are two comparative forms in English: the comparative which compares exactly two things, and the superlative which compares three or more things. Strictly speaking the term comparative only refers to the second degree, but the term comparatives as an umbrella term is used for both the comparative and the superlative.
English has two ways of forming comparatives. Synthetic comparatives are formed by adding the suffixes -er and -est to the base adjective:
A bright day
A brighter day (Comparative)
The brightest day (Superlative)
Analytic comparatives are formed by adding the word more or most before the adjective:
A miserable day
A more miserable day (Comparative)
The most miserable day (Superlative)
There is no strict rule which determines which adjectives are formed with the analytic comparative and which use the synthetic comparative. In general, native Germanic adjectives which are monosyllables or which end in -y use the synthetic comparative. Latinate adjectives, other borrowed adjectives, neologisms, and polysyllabic adjectives usually use the analytic comparative.
Adverbs also form comparatives, but they only use the analytic comparative:
A closely watched match
A more closely watched match
The most closely watched match