Cleverer-the cleverest
Sillier-the silliest
Blacker-the blackest
Thicker-the thickest
Merrier-the merriest
Wider-the widest
More expensive-the most expensive
More modern-the most modern

Tom is clever.Ann is cleverer than Tom.Jack is the cleverest of all.
It is a silly joke.This joke is sillier than that joke.These are the silliest jokes of all.
My hair is black.Her hair is blacker than night .My friend's hair is the blackest.
I have a thick blanket.Her blanket is thicker than mine. His blanket is the thickest.
Kate is a merry girl.I am merrier than Kate.Liz is the merriest of all.
The first river is wide.The second one is wider than the first one.The third river is the widest of all.
Jane bought an expensive dress.Mary bought more expensive dress.Nicole bought the most expensive dress of all.
Moscow is a modern city.Tokyo is more modern city than Moscow.Singapore is the most modern city of all.