Grammar: the Adjective

Adjectives are words expressing properties and characteristics of objects (e.g. blue, simple, progressive, etc.) and, hence, qualifying nouns. Grammatically, four features are generally considered to be characteristic of adjectives:

1) their syntactic function of attributes;
2) their syntactic function of predicatives;
3) their taking of adverbial modifiers of degree (e.g. very);
4) their only grammatical category — the degrees of comparison.

Adjectives in English do not change for number or case.

Degrees of Comparison

There are three degrees of comparison: positive (or absolute), comparative and superlative. There are three ways of forming the comparative and the superlative degrees: synthetic, analytical and suppletive.

Synthetic: by adding the suffix –er to the comparative degree and the suffix -est to the superlative degree.

Types of adjectives forming their degrees of comparison in a synthetic way:

1) monosyllabic: great ― greater ― greatest;
2) disyllabic: ending in –y: lovely ― lovelier ― loveliest;
-ow: narrow ― narrower ― narrowest;
-le: simple ― simpler ― simplest;
-er: clever ― cleverer ― cleverest;
-some: handsome ― handsomer ― handsomest;

Analytical: the comparative degree is formed by adding the word more, the superlative ― most: careful ― more careful ― most careful; personal ― more personal ― most personal; tired ― more tired ― most tired

Suppletive (Irregular):

good ― better ― best;
bad ― worse ― worst;
little ― less ― least;
many ― more ― most;
near ― nearer ― nearest (for distance) // next (for time);
far ― farther ― farthest (for distance) // further ― furthest (for time & distance);
old ― older ― oldest (for age) // elder ― eldest (for seniority);
late ―later - latest (for time)// last (for order);

Comparison of compounds.

Compound adjectives can be inflected in two ways:
1) the first element is inflected if it is an adjective or an adverb (regular with well-): well-known — better-known — best-known;
2) an analytical way: kind-hearted — more kind-hearted — most kind-hearted. The following adjectives do not form degrees of comparison:
1. Limiting qualitative adjectives which single out or determine the type of things or persons, such as: previous, middle, left, childless, medical, dead, etc.
2. Relative adjectives such as: wooden, woolen, leathern.
3. Adjectives with comparative and superlative meaning which are of Latin origin: former, inner, upper, junior, senior, prior, superior, minimal, etc.

Word combinations with less and least are not considered to be analytical forms of degrees of comparison. Remember the phrase ― the lesser of two evils, lesser is not a comparative degree but an adjective meaning ‘not as great as other(s)’.

More on English grammar I get from here: http://uastudent.com/category/english/