Internal Inflection

the expression of grammatical meanings by changing the structure of the root—for example, the Russian sobirat’ (imperfective aspeci)-sobrat’ (perfective aspect), “to collect”; the German ziehen, “they pull”-zogen, “they pulled”; and the English “foot” (singular)-“feet” (plural). Internal inflection may be used together with external inflection—that is, with the expression of grammatical meanings through the use of affixes. Such phenomena as the formation of the Arabic “broken” plural by changing the vowels of the stem—kitāb (“book”)-kutub (“books”)—are approximately regarded as the addition of various discontinuous affixes (-i-ā-, -u-u-) to the triconsonantal root k-t-b rather than as internal inflection.