Superlative adjectives express the highest or lowest degree of a quality within a group. In English, superlatives often appear with "the" because they identify a unique extreme. They are used to compare one item to all others in the set being described. The form of the superlative depends on the adjective’s length and structure.

For most one-syllable adjectives, form the superlative by adding "-est" to the base adjective. If the adjective ends in a single consonant preceded by a single vowel, double the final consonant before adding "-est." If the adjective ends in "e," add only "-st."

Rule
Most one-syllable adjectives form the superlative with -est.
Adjectives ending in e form the superlative with -st.
Adjectives ending consonant-vowel-consonant double the final consonant before -est.

Many two-syllable adjectives form the superlative with "the most." Two-syllable adjectives ending in "y" usually change "y" to "i" and add "-est." Some two-syllable adjectives can use either "-est" or "the most," but "-est" is more common with certain patterns such as endings in "-y," "-le," and "-ow."

Rule
Two-syllable adjectives often form the superlative with the most.
Two-syllable adjectives ending in y usually take -iest.
Two-syllable adjectives ending in le or ow may take -est in common usage.

Adjectives with three or more syllables form the superlative with "the most" before the adjective. The adjective itself does not change its spelling in this pattern. This rule also applies to many two-syllable adjectives that do not commonly take "-est."

Rule
Adjectives with three or more syllables form the superlative with the most.
The adjective does not change spelling when used with the most.
The most can be used for clarity with longer or less common adjectives.

Some common adjectives have irregular superlative forms that do not follow the regular "-est" or "the most" patterns. These forms must be memorized because they are exceptions to the usual rules. They are extremely frequent in natural English.

Word/Phrase	Definition
best	The superlative form of good.
worst	The superlative form of bad.
least	The superlative form of little when meaning amount.
most	The superlative form of much and many.
furthest	An irregular superlative of far.
farthest	An irregular superlative of far.

Superlative adjectives in English are formed with "-est" for most short adjectives and with "the most" for longer adjectives. Irregular forms such as "best," "worst," and "most" do not follow the regular patterns. Superlatives identify the highest or lowest degree within a group and are usually used with "the" to specify a unique reference.