The article represents structural semantic analysis of the grammatical number of nouns in the Indo-European (English, German), Semitic (Arabic, Hebrew), and Altai (Tatar, Japanese) languages. The category of number comprises numerous phenomena, including some transitive and historical aspects, which complicate and enrich the system of language. Several controversial features of the category may be pointed out, especially those concerning the phenomena of collectiveness, duality, segmentation, etc. The idea of plurality is reflected in the mind of different people in the many-sided way. In the Indo-European languages there are mass nouns that occur only in the singular. Also, there are countable nouns that occur only in the plural. The special attitude of the Semitic languages towards the category of number can be noticed in the formal interpretation of the concept "singularity-plurality". Their graphic style of thinking penetrates the grammar of Arabic and Hebrew and is reflected in the category of number. In Tatar the singular and plural forms are distinguished. There are a lot of number affixes. Japanese does not grammatically differentiate between singular and plural forms. So, the isomorphic and allomorphic traits of the number category reflect universal and unique language verbalization of different cultures, revealing people's world outlook, their traditions and history.