Dissatisfaction is expressed with the theories generally offered as explanation for the development of the IIwy verbs in West Semitic. As a result, recourse is made to an internal reconstruction of the relevant groun as it occurs in Classical Arabic, in terms of its lin guistic context in that language. From this the conclusion is drawn that mid vowels (e: and o:) existed as phonemes in these verbs at an earlier stage. The comparative data from Ethiopic and Hebrew is then examined, and found to be in broad agreement with the Arabic conclusions. Reasons for the loss of the phonemes, and the circum stances of that loss, are briefly discussed.