Many adjectives do not admit of comparison by terminations, and are only compared by more and most, as, benevolent, more benevolent, most benevolent.
All adjectives may be compared by more and most, even when they have comparatives and superlatives regularly formed; as, fair, fairer, or more fair; fairest, or most fair.
In adjectives that admit a regular comparison, the comparative more is oftener used than the superlative most, as more fair is oftener written for fairer, than most fair for fairest.
The comparison of adjectives is very uncertain; and being much regulated by commodiousness of utterance, or agreeableness of sound, is not easily reduced to rules.
Monosyllables are commonly compared.
Polysyllables, or words of more than two syllables, are seldom compared otherwise than by more and most, as, deplorable, more deplorable, most deplorable.
Dissyllables are seldom compared if they terminate in some, as fulsome, toilsome; in ful, as, careful, spleenful, dreadful; in ing, as trifling, charming; in ous, as porous; in less, as, careless, harmless; in ed, as wretched; in id, as candid; in al, as mortal; in ent, as recent, fervent; in ain, as certain; in ive, as missive; in dy, as woody; in fy, as puffy; in ky, as rocky, except lucky; in my, as roomy; in ny, as skinny; in py, as ropy, except happy; in ry, as hoary.
Some comparatives and superlatives are yet found in good writers formed without regard to the foregoing rules; but in a language subjected so little and so lately to grammar, such anomalies must frequently occur.
So shady is compared by Milton.
She in shadiest covert hid,