The paper deals with the problem of expressing such category as animacy / inanimacy in some Indo-European languages (Latin, Ancient Greek and Russian) which have masculine / feminine gender distinction. The interaction of this category with case marking and the types of declension is under consideration. The paper also presents an attempt to place these categories in the framework of semantic typology of noun classification. The model of such a classification is presented, and the further analysis shows how one of the subtypes of this classification (to which all of the afore-mentioned languages belong) is still keeping animacy / inanimacy distinction after acquiring masculine / feminine subdivision. This distinction is found in the correlation between animacy and the case marking in Latin and Ancient Greek (zero- or sigma-inflection in the nominative case) and between animacy and the type of declension in Latin, Ancient Greek and Russian. This analysis allows us to highlight the semantic weight of declension, which is considered to be a formal category.