There have been controversies since the ancient time, definition and nature of literature as well as its domain and practical applications. Some scholars have applied the term in a moral sense, whereas some others have used it in the literary sense and still others have used it in both senses. However, today literature has achieved great importance through developing ties with new sciences such as psychology, linguistics and literary criticism. A brief review of the western literary nations and theories and the study of literary views of Plato, Aristotle, Sidney, Drydon, Johnson, Colleridge and others reveal that, first of all, the literary movement that was initiated by Aristotle and lived up to the time of Collridge was in line with the European culture. That is to say, if at the beginning their views on moral instructions had a special sense and function, in the literary domain, it would lose its influence through the ages and the theme of moral instructions has been substituted by the theme of ‘enjoyment’. Second of all, in defining poetry and literature, we face problems and shortcomings which make it difficult to generalize the views to great works of literature in the world. This paper reviews and elaborates the western literary theories and the way in which they shifted from a theme of ‘moral teachings’ to ‘enjoyment’ and from ‘enlightment’ to ‘ ambiguity’. By drawing upon the theories of Khaje-Nasir, Kroche, and the concept of ‘intuition’ efforts have been made to offer a comprehensive and more functional definition of literature with the aim of paving the way to settle most of our literary and scientific controversies.