The article shows that relying on the abstract theory of language ("psychosistematics" of G. Guillaume) while considering problems of comparative linguistics according to the data of the contemporary Indo-European studies is anachronic and, therefore, unjustified. As shown by the empirical material, the most ancient in the Indo-European voice system was not the opposition of active/passive, but the active/inactive one, later transformed into the opposition of the active/middle voice. Furthermore the psychosistematics distorts some significant and commonly recognized achievements of Indo-European studies: 1) in the ergative (previous to inflective) period the agreement of nouns and adjectives was characterized by verbal-noun syncretism; 2) the formation of the category of gender in the Indo-European has its semantic basis; 3) the early period of Indo-European was characterized by the existence of undifferentiated nominal stem prior to the formation of a case system with its nominative-accusative case oppositio