Adjectives change in form (tall, taller, tallest) to show comparison. They are called the three Degrees of Comparison.
The Adjective tall is said to be in the Positive Degree.
The Adjective taller is said to be in the Comparative Degree.
The Adjective tallest is said to be in the Superlative Degree.
Formation of Comparative and Superlative
Most adjectives of one syllable, and some of more than one, form the Comparative by adding er and the Superlative by adding est to the Positive.
Positive: Clever
Comparative: Cleverer
Superlative: Cleverest
When the Postive ends in e, only r and st are added.
Positive: Large
Comparative: Larger
Superlative: Largest
When the Postive ends in y, preceded by a consonant, the y is changed into i before adding er and est.
Positive: Heavy
Comparative: Heavier
Superlative: Heaviest
When the Postive is a word of one syllable and ends in a single consonant, preceded by a short vowel, this consonant is doubled before adding er and est.
Positive: Thin
Comparative: Thinner
Superlative: Thinnest
Adjectives of more than two syllables form the Comparative and Superlative by putting more and most before the Positive.
Positive: Difficult
Comparative: More Difficult
Superlative: Most Difficult
The following Adjectives are compared irregularly, that is, their comparative and Superlative are not formed from the Positive:
Positive: Bad
Comparative: Worse
Superlative: Worst
This is called Irregular Comparison.