Corpus Areopagiticum, along with the scholia written by John of Scythopolis and Maximus the Confessor provides a modern researcher with an opportunity to reconstruct concepts of reason and other features of human intellectual activity which were developed in philosophical and theological discourse of the early Middle Ages (6th-7th centuries CE). The paper will reveal major characteristics of reason (nou=j) throughout the hierarchy of heavenly and earthly beings, as they are presented in the scholia mostly. The choice of scholia is determined by the fact that, unlike the text by Pseudo-Dionysius itself, the commentary is less poetic but more logically organized and contains numerous definitions of different mental phenomena (e.g., memory, imagination, opinion, knowledge) as well as many similar passages devoted to these phenomena, which allows to consider them from different angles. Thus, reason has different characteristics referring to different levels of the World. God, who is Reason in Its highest entity, has it undifferentiated: everything is in His Mind before it comes into existence. The heavenly beings, the members of the celestial hierarchy, have to obtain knowledge about God's will and plans, but can do it by a single act of revelation, which is possible only for exceptional humans and in exceptional circumstances. As for other human beings, they perceive the world piece by piece and have to apply various logical instruments to restore the wholeness lost in the process of emanation.