The full forms of triconsonantal roots could be modified by the suffixion of the extra vowel (SD/422), for example: ✶kalba < √KALAB. With subordinate-vowel-variation, the word could also end in a basic vowel different from the characteristic vowel: ✶kalbi, ✶kalbu (SD/422).

Where there was a suffixed vowel, there was never a vowel between the second and third consonant. Therefore, primitive words of the form **kalaba were not possible (SD/422).

This rule did not apply to biconsonantal roots, because their full forms already had a suffixed vowel, such as ✶ziri < √ZIR.