Derivation is the process of forming new words from existing words through the addition of affixes. There are two types of bound morphemes in English: inflectional morphemes, which do not change the word class, and derivational morphemes, which can change the word class with or without changing the meaning. Derivational affixes are divided into two classes - class 1 affixes typically affect the phonology of the base word, while class 2 affixes are phonologically neutral. Derivation is constrained and some affixes can only be added to words of a certain origin or phonological structure. Complex derivation can change the grammatical category of a word through multiple affixations.