Two kinds of consonant modifications could occur when deriving a primitive word from a root: nasal-infixion and consonant-doubling. These modifications could only apply to an isolated basic consonant, not to a consonant cluster. Both modifications were most frequently applied to the final consonant, but could apply to the medial consonant. Only consonant doubling could be applied to the initial consonant, and then only rarely.

When these modifications were applied to the final consonant of a word without a suffixed vowel, the result was a consonant cluster, which was not allowed for the final-consonants of a Primitive Adûnaic word, such as: ✶Ad. √KULUB > **kulumb or **kulubb. In such cases, a vowel suffix was needed to produce a valid word. Since there were already two instances of the characteristic-vowel in such words, the third vowel needed to be a different basic vowel, as per the rules of subordinate-vowel-variation, for example: ✶kulumba, ✶kulumbi or ✶kulubba, ✶kulubbi.