**Derivational morphology** describes how a language includes different word forms using prefixes and suffices, for example turning a verb or adjective into a noun with a suffix. Derivational morphology is characterized by - quasi-systematicity: systematic rules with many broken rules - irregular meaning change: adding the same suffix may result in non-parallel meaning changes - changes of word class: the same word may be one of multiple word classes Languages vary widely in their derivational morphology with important consequences for natural language processing systems. - Isolating (analytic) languages tend towards one morpheme per word. - Synthetic languages (e.g., Arapaho) jam many morphemes into a single word. - Polysynthetic languages can jam entire sentences into a single word. - Agglutinating languages concatenate many affixes to a single stem (e.g., German, Turkish). - Fusional languages allow morphemes to change their form upon attachment (making it difficult to isolate stems).