Phonological distinctions vanish in the course of the evolution of a language, but in diachronic phonology it is known that the distinctive oppositions involved do not necessarily disappear as a consequence thereof. Certain effects brought about by the ancient phonemes while they were still articulatorily different do survive after the originally distinct articulations have merged into one. The surviving effects are customarily called ‘reflexes’, that is, of the phonemes now extinct, and it is they that permit us to assume with a considerable degree of certainty that the distinctions now perceivable by virtue of the surviving effects were once vested in different phonemes in the same language. The doctrine of phoneme reflexes has contributed immensely to an ampler, more complete, and more refined knowledge of the sound system of the ancient Indo-European languages. In Semitics, however, this line of investigation has hitherto been much less exploited. While there can be no doubt that we have a fairly good knowledge of what might be termed ‘the common Semitic sound system’, such insights can only tell us what phonological distinctions exist in one historical Semitic language, while being absent from another, and how correspondences should be drawn up between them. The advantage, however, of the study of reflexes is that it affords insights into the mechanism of one and the same language and permits inferences on historically unattested distinctions as well as the reconstruction of a stage of a language prior to its earliest written documentation. We can grasp here the real difference between comparison and reconstruction: while comparison enlightens us as to how languages differ, it cannot make us see the true identity or physiognomy of any given language. This latter task is dependent upon the doctrine of reflexes. If certain otherwise common Semitic distinctions involving pharyngals are reflected in Early Akkadian as neatly regulated mechanisms of vocalic patterns, we must infer that it is not true to say that Akkadian is set apart from other Semitic languages by the absence in it of pharyngal articulations, because these articulations, since they left traces, could not have been absent in that language in its earliest stages. The identity of Akkadian will, therefore, have to be established on the ground of the presence, rather than the absence, of a certain statable number of pharynsal phonemes.