159. The comparative is formed by adding -er, and the superlative by adding -est, to the simple form; as, red, redder, reddest; blue, bluer, bluest; easy, easier, easiest.
Substitute for inflection in comparison.
160. Side by side with these inflected forms are found comparative and superlative expressions making use of the adverbs more and most. These are often useful as alternative with the inflected forms, but in most cases are used before adjectives that are never inflected.
They came into use about the thirteenth century, but were not common until a century later.
Which rule,— -er and -est or more and most?
161. The English is somewhat capricious in choosing between the inflected forms and those with more and most, so that no inflexible rule can be given as to the formation of the comparative and the superlative.
The general rule is, that monosyllables and easily pronounced words of two syllables add -er and -est; and other words are preceded by more and most.
But room must be left in such a rule for pleasantness of sound and for variety of expression.
To see how literary English overrides any rule that could be given, examine the following taken at random:—
From Thackeray: "The handsomest wives;" "the immensest quantity of thrashing;" "the wonderfulest little shoes;" "more odd, strange, and yet familiar;" "more austere and holy."