The article presents and systematizes materials that were previously only casually touched upon in studies on ancient Greek verbal vocalism. Analyzing the material, the author comes to the conclusion that the alternations being the object of the study do not have synchronous phonetic conditioning and can be referred to the sphere of morphology. The article proposes new parameters for the classification of these alternations: the qualitative or quantitative nature of the alternative, the quantity and quality of the positions of the derivative (marked) alternant, the phonetic quality of the alternating members. It is proved that for the considered section of the morphological system of the ancient Greek language, the decisive factor of the stratification of positions is markedness, which is determined by the relations between members of the alternative series. The article also establishes the lexical representation of each of the distinguished classes of alternations.