The paper considers semantic categories presented in the ideographic discourse. Research material includes the information retrieval thesauruses reflecting scientific information activities and functional and ideographic dictionaries representing the discourse of training in writing school compositions and the epistolary discourse (letters of Russian writers). The author regards semantic categories as sign units (sign formations) whose content plane is general concepts, and denotation is various language (sign) means forming this general concepts. The article shows that semantic categories, as the result of categorization, reflect properties of the discourse - the functional and communicative field in which it appears, characteristics of the speech subject, character of the relation of the author of the text to its topic and to the addressee, interaction with the language code. The paper discusses the technique of semantic category choice, the formation of their list, their participation in creating the classification schemes of concepts, the opportunities of using ideographic dictionaries to solve linguistic and pedagogical tasks. The article provides the conclusions on the existence and nature of system communications of ideographic semantic categories with such cognitive aspects of the language as a problem situation in word using and understanding, classification of lexical units and concepts, psychology of thinking in language forms, specifics of extralinguistic factors in scientific and language activity in different private discourses.