To make the comparative form ('stronger' or 'more delicious'), the first thing we need to know is the number of syllables in the adjective.
Normally if an adjective has one syllable, we add 'er' to make the comparative form.
There are some spelling changes. If the adjective ends in 'e', we don't add another 'e', just 'r'.
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 'more' with, even though they only have one syllable. Adding -er is incorrect for these verbs.
Some adjectives with two syllables use 'more'.
However, some two syllable adjectives can use 'er'.
For adjectives with two syllables that end in 'y' we normally add 'er' (y generally changes to i).
Adjectives that have more than two syllables need to use 'more' to form their comparative.
There are also some irregular adjectives. We simply need to memorize them.