Even the earliest Arab grammarians emphasized the distinctiveness of the verb stems with hamza and w or y as one of the root consonants. Similar attention was paid to the verbs of which the second and third radical are identical. A quite substantial part of Sībawaihi’s (750-793) Al-Kitāb deals with these issues. Sībawaihi presents in detail all the possible phonetic changes that result from such configurations of consonants in the Arabic verb stems. He does not limit himself to a rigid and strictly normative description. When drawing the boundaries of linguistic correctness, he takes into consideration local colors of the Arabic tongue of Naǧd in the east and that of Al-Ḥiǧāz in the west. When describing the mechanism of phonetic transformations, he often points to the reasons that lie behind them. Not infrequently, he resorts to examples from the spoken Arabic