Word-formation in modern english
The word is not the smallest unit of the language. It consists of morphemes. The morpheme may be defined as the smallest meaningful unit which has a sound form and meaning and which occurs in speech only as a part of a word.
Word formation is the creation of new words from elements already existing in the language. Every language has its own structural patterns of word formation.
Morphemes are subdivided into root - morphemes and affixational morphemes.
The root morpheme is the lexical center of the word. It is the semantic nucleus of a word with which no grammatical properties of the word are connected, Affixational morphemes include inflections and derivational affixes.
Inflection is an affixal morpheme which carries only grammatical meaning thus relevant only for the formation of word-forms (books, opened, strong-er).
Derivational morpheme is an affixal morpheme which modifies the lexical meaning of the root and forms a new word. In many cases if adds the part-of-speech meaning to the root (manage-ment, en-courage, fruit-ful)
Morphemes which may occur in isolation and function as independent words are called free morphemes (pay, sum, form).