DEGREE OF COMPARISON

In English grammar the degree of comparison of an adjective or adverb that describes the relational value of one thing with something in another clause of a sentence. An adjective may simply describe a quality, (the positive); it may compare the quality with that of another of its kind (comparative degree); and it may compare the quality with many or all others (superlative degree). [1] In other languages it may describe a very large degree of a particular quality (in Semitic linguistics, called an elative).
The degree of comparison may be expressed morphologically, or syntactically. In English, for example, most monosyllabic and some disyllabic adjectives have morphological degrees of comparison: green (positive), greener (comparative), greenest (superlative); pretty, prettier, prettiest; while most polysyllabic adjectives use syntax: complex, more complex, most complex.
1. The positive degree is the most basic form of the adjective, positive because it does not relate to any superior or inferior qualities of other things in speech.
2. The comparative degree denotes a greater amount of a quality relative to something else. The phrase “Anna is taller than her father” means that Anna's degree of tallness is greater than her father's degree of tallness.
3. The superlative degree denotes the most, the largest, etc., by which it differs from other things.
Rhetorical use of unbalanced comparatives
In some contexts, such as advertising or political speeches, absolute and relative comparatives are intentionally employed in a way that invites a comparison, and yet the basis of comparison is not established. This is a common rhetorical device used to create an implication of significance where one may not actually be present. Although such usage is common, it is sometimes considered ungrammatical.[citation needed]
For example:
• Always!
• Why pay more?
• We work harder.
• We sell for less!
English usage
Traditional English grammar uses the comparative form when comparing exactly two things, and the superlative when comparing three or more, but in informal usage this may not hold.[clarification needed]
Positive Comparative Superlative
Good Better Best
Beautiful More Beautiful Most Beautiful
Big Bigger Biggest
Tall Taller Tallest
Sincere More Sincere Most Sincere
Small Smaller Smallest

source: http://en.wikipedia.org/wiki/Degree_of_comparison