What’s the difference between comparative adjectives and superlative adjectives?
There are three forms of comparison adjectives in English: positive, comparative, and superlative.

Positive
This is the normal form of the adjective.
➜ E.g. Jim is strong.

The adjective in this example is strong. 

Comparative
This is the form used when comparing two nouns.
➜ E.g. Jim is stronger than Adam.

Comparative adjectives end in ‘er’ and are followed by the word ‘than’.

The comparative adjective in this example is stronger. The nouns being compared are Jim and Adam. 

Superlative
This is the form used when comparing a noun with other nouns in a group. It indicates that the quality or quantity is at its highest.
➜ E.g. Jim is the strongest in the class.

Superlative adjectives end in ‘est’ and come after the article ‘the’.

The superlative adjective in this example is strongest. Jim is being compared to everyone else in his class.

There are several rules we need to follow when forming comparative and superlative adjectives. These rules depend on the letter in the adjective or the number of syllables.

Here is a simple summary of the rules:

One syllable adjective
✔︎ Comparative ⟶ add er.
✔︎ Superlative ⟶ add est.

E.g. Strong – Stronger – Strongest 

Adjective with a consonant, short vowel + consonant spelling
✔︎ Comparative ⟶ double the final consonant and add er.
✔︎ Superlative ⟶ double the final consonant and add est.

E.g. Big – Bigger – Biggest 

Adjectives ending in -e
✔︎ Comparative ⟶ remove the letter e & add er.
✔︎ Superlative ⟶ remove the letter e & add est.

E.g. Large – Larger – Largest 

Adjectives ending in -y
✔︎ Comparative ⟶ remove the letter y, add the letter i & add er.
✔︎ Superlative ⟶ remove the letter y, add the letter i & add est.

E.g. Happy – Happier – Happiest  

Two syllables
✔︎ Comparative ⟶ add er or add ‘more’ before the word.
✔︎ Superlative ⟶ add est or add ‘most’ before the word.

E.g. Gentle – Gentler/More gentle – Gentlest/Most gentle  

Three or more syllables
✔︎ Comparative ⟶ add ‘more’ before the word.
✔︎ Superlative ⟶ add ‘most’ before the word.

E.g. Expensive – More expensive – Most expensive  

Irregular forms
✔︎ There are many irregular forms that don’t follow the rules; therefore, it’s important to learn them.

E.g. Good – Better – Best