The usage of modal verbs are reviewed in corpus of six texts from 6th Hegira (Atbat-al Katba, Asrar al-Tawhid, Tazkerat-al Ulia, Maqamat-e Hamidi, Kelileh and Demneh and Rahat-al Sudur). The results show that the usage amount of these verbs is considerable among other kinds of verbs. In modal constructs, modal adjectives and adverbs help enrich the meaning of necessity, possibility, capability and wanting in addition to modal verbs. Regarding the contextual and functional meaning, the concepts of commitment, necessity and … are more considerable in a work like Atbat-al Katba. Political, narrative and mystical insights, character, social power and status are among the factors the affect their amount of application and degree of modal elements. The study shows that the difference of genres brings about even little differences. The depiction of general features of a period style and personal experiences of every author are related to a subject which is dealt with in this study.