Conventions of Composition Rule 149
Rules: Comparatives (formed by adding er or preceding with more) must be used to compare two items. Superlatives (formed by adding est or preceding with most) must compare three or more.
Note: It is incorrect to use both the preceding word and the ending at the same time. Use the ending for words of one or two syllables, the word for more syllables.
Examples:
Correct: He is taller than his sister, but their mother is the tallest in the family.
Correct: Nat has the most adorable kitten of any I've ever seen.
Correct: More students read Fitzgerald's work than Milton's, but most students read Shakespeare's.
Practice using comparatives and superlatives:
Of my sister and me, I stand the tallest.
Sasha has the most hardest last name to pronounce.
Terry and Val, their classmates all agree, have the most best enunciation on the Debate Team.
Resources for further explanation of comparatives and superlatives:
Khan Academy's Comparative and The Superlative
British Council's Comparative and Superlative Adjectives
Grammar Girl's podcast (from 6:53-13:45) Quick and Dirty Tips and Part Two (from 11:25-16:42)