While most adjectives take an –er suffix in their comparative form, many retain their positive form and take ‘more’ or ‘less’ before them.
As a pet, a dog is more faithful than a cat. (not faithfuller)
She is more hard-working than her brother. (not harder-working)
Adjectives with two or more syllables usually form their comparative degree with ‘more’ or ‘less’.
Difficult – more difficult/less difficult
Intelligent – more intelligent/less intelligent
Foolish – more foolish/less foolish
Normal – more normal/less normal
Nervous – more nervous/less nervous
Important – more important/less important
Active – more active/less active
The present and past participles of verbs used as adjectives (participial adjectives) build their comparative degree with ‘more’ or ‘less’.
Interesting – more interesting/less interesting
Concerned – more concerned/less concerned
Worn – more worn/less worn
Cooked – more cooked/less cooked
The comparative degree of adjectives is usually followed by ‘than’ to make the comparison, but the following are a few exceptions to this:
Junior + to
Senior + to
Inferior + to
Superior + to
Preferable + to
These comparative degrees of the adjectives do not take ‘more’ or ‘less’ before them. The adjectives ‘good’, ‘bad’ and ‘far’ are special cases with the following comparative and superlative degrees:
Adjectives that take ‘more’ or ‘less’ to build their comparative form take ‘the most’ or ‘the least’ to build their superlative form.
Difficult-more difficult-the most difficult
Important-more difficult-the most difficult
Concerned-less concerned-the least concerned
Active-less active-the least active.