Degrees of comparison of adjectives example: hot- hotter- the hottest interesting- more interesting- the most interesting helpful, simple, happy, terrible, narrow, severe, difficult, untidy, modern, warm, low, big, tender, expensive, wise.

helpful - more  helpful  - the most  helpful
simple - simpler - the simplest 
happy - happier - the happiest
terrible - more  terrible - the most  terrible
narrow - narrower - the narrowest
severe - severer - the severest
difficult - more  difficult - the most  difficult
untidy  - untidier - the untidiest
modern -  more modern - the  most modern
warm - warmer - the warmest
Low - lower - the  lowest
big - bigger - the  biggest
tender — more tender — the most tender
expensive - more expensive - the most expensive
wise — wiser — the wisest