In grammar, the comparative of an adjective or adverb is the greater or lesser form of that adjective or adverb. The comparative of "hot," for example, would be "hotter." Superlatives are simply the greatest form of an adjective or adverb - "hottest," to use the current example. Comparatives and superlatives are common grammatical mechanisms and understanding them is important for effective reading comprehension and linguistic competency.
One-syllable Adjectives
One-syllable comparative adjectives are formed by adding -er to the root adjective. "Tall" would become "taller" and "long" would become "longer." For the superlative an -est is added to the end of the adjective. "Tall" would be "tallest" and "long" would be "longest." In sentence form, "Craig is taller than Clair" is the use of a comparative and "Vicky's story is the longest" uses a superlative. If there is a single vowel followed by a single consonant at the end of the root adjective, like "wet," the last letter is doubled before adding the suffix ("wetter" and "wettest").
Two-syllable Adjectives
Two-syllable adjectives are usually even easier than one-syllables. The comparative is formed by putting "more" in front of the adjective ("pleasant" becomes "more pleasant"). To get the superlative, "most" is used instead of "more" ("most pleasant"). It gets tricky when the two-syllable adjective ends in "y." In those instances the "y" becomes an "i" and the rules of one-syllable comparatives and superlatives are applied. In a sentence: Dan was happier (comparative); Sarah was happiest (superlative).
Adjectives with Three or More Syllables
Adjective with three or more syllables follow the two syllable rules and use "more" for the comparative and "most" for the superlative. Kirsten is "more satisfied" than Dale is the comparative, and Kathryn is the "most satisfied" of everybody is the superlative.
Exceptions
Some adjectives are irregular and have individual rules governing their comparative and superlative forms. "Many" is an obvious example because of its use with standard multiple comparative and superlatives. Its comparative is "more" and its superlative is "most." "Good" is another irregular adjective (comparative: "better," superlative "best"). Some irregular adjectives such as "clever" or "friendly" can use interchangeable rules (both -er and "more").
Comparative and Superlative Adverbs
For adverbs that are the same as their corresponding adjective such as "hard" and "fast", the comparative and superlative follow the same rules as with adjectives (add -er for comparative and -est for superlative.) For -ly adverbs such as "quietly" and "carefully" (as opposed to adjectives "quiet" and "careful"), add "more" for comparative and "most" for superlative" ("more quietly" or "most carefully," for example).