Through an examination of the Arabic emphasizing particle la- and a set of elements in the other Semitic languages to which it is akin, this study investigates the early Semitic sonorant phonemes and their development in the descendant languages. This linguistic study is concerned with the role of the emphasizing particle la- (known as lām al-ta'kīd) in the grammatical traditions of Classical Arabic, as well as with the question of the historical relationship connecting this particle to a set of elements in several other Semitic languages showing comparable forms and functions. Although these particles have hitherto seemed to defy a coherent reconstruction, the very complexity of the data to which they attest proves to provide a key to their interpretation. They represent a critical first step in the refining of our understanding of the history of the Semitic sonorant phonemes.