It has been illustrated, by no means exhaustively, the wide variety of tasks that derivation can play. In this respect, derivation contrasts with inflection in English. By comparison with most other European languages, such as French and German, English has few inflectional affixes; however, English is at least as rich as French and German in its derivational resources. Some of the reasons for this are historical.

Because of the versatility of derivation in English, one might have expected that many of the processes involved would have been sufficiently predictable in both their application and their meaning so that the lexemes thus derived would not count as lexical items. However, only four of the affixes that we have discussed yield large numbers of lexemes that one would not expect to find listed in a dictionary, namely adverb-forming -ly, negative adjectival un- and nominal -ness and -ing. It is as if, despite the fact that lexemes are not necessarily lexical items, there is a deep-seated readiness to allow them to become lexical items – that is, to treat the products of all derivational processes, even the most general and semantically predictable ones, as potentially quirky. Why so? Underlying this puzzle are big questions about the status of the word as a linguistic unit – questions too big and controversial to be tackled here.