Superlative adjectives are used to describe an object or person which is at the upper or lower limit of a quality (the tallest, the smallest, the fastest, the highest). They are used in sentences where a subject is compared to other objects or people.
If an adjective has one syllable, we usually add 'est' to make the superlative form.
There are some spelling changes. If the adjective ends in 'e', we don't add another 'e', just 'st'.
If there is one vowel followed by one consonant at the end of the adjective, we often double the consonant.
There are some adjectives that we need to use 'most' with, even though they only have one syllable. Adding -est is incorrect for these verbs.
Some adjectives with two syllables use 'most'.
However, some two syllable adjectives can use 'est'.
For adjectives with two syllables that end in 'y' we normally add 'est' (y generally changes to i).
Adjectives that have more than two syllables need to use 'most' to form their superlative.
There are also some irregular adjectives. We simply need to memorize them.