This article will only explain how to make comparative/superlative adjectives.

You can learn more about how to use them in comparative sentences here. 

The first step to understanding comparative/superlative adjectives is to divide all adjectives into four categories:

1. One syllable adjectives;
2. Two syllable adjectives;
3. Longer Adjectives;
4. Irregular Adjectives.

The simple rule is that you use -er/-est for short adjectives, more/most for long adjectives, and -ier/iest for adjectives ending with -y. There are also a few irregular adjectives.   

There are more detailed explanations and breakdowns, with examples, for each category below:

One Syllable Adjectives

The basic rule is that you ad -er/-est to one-syllable adjectives

If the adjective ends with an -e, you only have to add -r/st

If the adjective ends with one vowel and one consonant, the consonant becomes a double consonant followed by -er/-est

Two Syllable Adjectives

The rules for two-syllable adjectives are the most complicated. In some case it is very difficult to know how to make the comparative/superlative, but the tables below should give you an idea. In some cases, you will still have to use a dictionary, because the adjective isn't covered by a rule.

If the adjective ends with -y, you add -ier/-iest as shown in the examples below

Note: With some longer adjectives ending with-y, such as unhappy or untidy, you can also either add -ier/-iest or use more

With some other two-syllable adjectives, especially if they end with an unstressed vowel, you add -er/-est

If the adjective ends with -ed, -ing, -ful, or -less, you have to use more

With many other two-syllable adjectives, such as polite or common, both ading -er/est or using more is possible. With others only more is acceptable. There isn't a simple rule in these cases and the best way to find out is to look the word up in a good dictionary.

Longer Adjectives

With all adjectives that have three or more syllables, you have to use more (except some that end with -y).

Irregular Adjectives

There are only a few adjectives that are irregular