The history of the genre theory dates back to the genre classificatory system of Plato and Aristotle that classified literary works–epic, lyric, and dramatic genres–according to enunciative modes; i.e. according to the enunciative modes that is represented in author or speaker’s discourse. In modern genre theory, “mode” denotes the thematic aspects of literary genres. When we say that this novel is tragic, it means that its genre is novel its mode is tragic. The modal terms–such as tragic, epic, heroic, gothic, lyrical, comic–are not dependent to the structural and formal aspects of the literary genres. This study aims to find out how some literary genres such as tragedy, comedy, epic, and lyric become so wide spread that their thematic features in adjective form are used to modify and describe other genres, while some other literary genres such as novel and short story cannot create their modes. Even though genres may disappear after some time, but their modes may survive in the longer run. The modes derive their life from genres, and their existence depends on genres. It should be noted, however, that there are some modes in English and Persian literature such as satire that is not derived from genres or literary forms.