In English, we need to make difference between long and short adjectives for example to create the comparative form and the superlative form, because they act differently.
a) SHORT ADJECTIVES:
Short adjectives are adjectives of one syllable or two syllable if they end by a '-y':
Examples:
one syllable: tall, short, long...
two syllables ending by '-y': happy, noisy, crazy...
b) LONG ADJECTIVES:
Long adjectives are adjectives of two or more syllables (except adjectives of two syllables ending by '-y').