How are the comparative and superlative forms of an adjective formed?

The comparative form of an adjective is formed by adding to the stem -ior (masculine and feminine)/-ius (neuter). The stem you should always use is the genitive stem. For example: longus,a,um - gen.stem: long - comparative: longior,longius pulcher,pulchra, pulchrum - gen.stem: pulchr - comparative: pulchrior, pulchrius The comparative form follows the third declension. Superlatives are instead formed by adding -issimus,a,um to the genitive stem. In case of adjectives ending in -er in the nominative, it is used the nominative masculine stem + rimus,a,um. They are then declined according to the 2nd and 1st declensions. Example: longus - gen.stem long - superlative: longissimus,a,um pulcher - nom.stem: pucher - superlative: pulcherrimus,a,um Furthermore six adjectives form their superlatives adding -limus,a,um to the genitive stem. Example: facilis - gen.stem: facil - superl. facillimus,a,um There are also irregular comparatives and superlatives, which don't follow the same stem of the positive form. bonus - melior - optimus malus - peior - pessimus parvus - minor - minimus magnus - maior - maximus multus - plus - plurimus