4.3.2. Inflectional and derivational morphemes

　 Bound morphemes are mostly affixes. Affixes are attached to free morphemes or stems (free morpheme + bound morpheme(s)) either to indicate grammatical categories or to form new words. Inflectional morphemes in modern English indicate case and number of nouns, tense and aspect of verbs, and degree of adjectives and adverbs. Specifically, modern English inflectional morphemes include:

　- 's, indicating the possessive case of nouns;
　- (e)s, indicating the plural form of nouns;
　- (e)s, indicating the simple present tense of verbs agreeing with a third person singular subject;
　- ed, indicating the past tense of verbs;
　- ing, indicating the progressive aspect of verbs;
　- er, indicating the comparative degree of adjectives and adverbs;
　- est, indicating the superlative degree of adjectives and adverbs.

　 Complementary with -er and -est are more and most, which are put before adjectives and adverbs composed of two or more syllables. -er and more, -est and most, are allomorphs.

　 Derivational affixes are bound morphemes added to existing forms to construct new words. According to their position in words, English affixes are divided into prefixes and suffixes (some languages have infixes, bound morphemes which are inserted into other morphemes). The process of putting affixes to existing forms to create new words is called derivation. Words thus formed are called derivatives. Derivation is one of the frequent ways of word formation, a point to be further taken up in the following section.