Page 146 - Practical English Usage 3ed - Michael Swan, Oxford

intelligent practical beautiful
more intelligent more practical more beautiful
most intelligent most practical most beautiful
comparison (3): comparative and superlative adjectives 137
The determiners little and muchlmany have irregular comparatives and superlatives:
little (see 329) less (see 320) least (see 318)
muchlmany (see 357) more (see 355) most (see 356)
Few has two possible comparatives and superlatives: fewerlless and fewestl least. See 320, 318.
3 two-syllable adjectives
Adjectives ending in -y have -ier and -iest. happy happrer happ~t
easy easkr eas~t
Some other two-syllable adjectives can have -er and -est, especially adjectives ending in an unstressed vowel, /11 or la(r)/.
TUlrrow simple clever quiet
narrower simpler cleverer qukter
narrowest simplest cleverest quietest
With many two-syllable adjectives (e.g. polite, common), -erl-est and morel most are both possible. With others (including adjectives ending in -ing, -ed, -fill and -less), only morelmost is possible. In general, the structure with morel most is becoming more common. To find out the normal comparative and superlative for a particular two-syllable adjective, check in a good dictionary.
4 longer adjectives
Adjectives of three or more syllables have more and most.
Words like unhappy (the opposites of two-syllable adjectives ending in -y) are an exception: they can have forms in -er and -est.
unhappy unhappier I more unhappy unhappiest I most unhappy
untidy untidier I more untidy untidiest I most untidy
Some compound adjectives like good-looking or well-known have two possible comparatives and superlatives.
good-looking better-looking
OR moregood-looking
well-known better-known
OR more well-known
5 more, most with short adjectives
best-looking mostgood-looking
best-known
most well-known
Sometimes morelmost are used with adjectives that normally have -erl-est. This can happen, for example, when a comparative is not followed immediately by than; forms with -er are also possible.
The road's getting more and more steep. (OR . • . steeper and steeper.) When we compare two descriptions (saying that one is more suitable or accurate than another), we use more; comparatives with -er are not possible.
He's more lazy than stupid. (NOT H~e'3 ~ier the", 3tftpid.)
In a rather formal style, most can be used with adjectives expressing approval and disapproval (including one-syllable adjectives) to mean 'very'.
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