Abstract
In the current study on premodern Iranian poetries, from the first century of the history of Persian literature to the period of literary return, it is seen that the imaginary forms used in the poetry of the poets of the third to fifth centuries AH are innovative and the product of their own poetic experience. But with the passage of time from the end of the fifth century onwards, poets, instead of incorporating images of their own personal experience and elements of nature and life into poetry, have always remained within the same images. The question that this research seeks to answer is: why from the end of the fifth century onwards (until the return period), the forms of imagination used in the poetry of Iranian poets are often imitative and repetitive, and devoid of any kind of innovation?
Extended abstract
By examining the poetry of pre-modern Iranian poets, from the first century of the history of Persian literature to the period of literary return, it can be seen that the images used in the poetry of poets of the third to fifth centuries AH are innovative and the product of their personal poetic experience. But over time, from the end of the fifth century onwards, poets, instead of incorporating images of the product of their personal experience and new elements of nature and life into poetry, have always remained within the same range of images of the poets of the past.
The question that this research seeks to answer is: why from the end of the fifth century onwards (until the period of literary return), the forms of imagination used in the poetry of Iranian poets are often repetitive and any innovation is out of the realm of the ancients? Thomas Kuhn's theory of paradigm can be used to answer this question. According to this theory, scientific transformations alternate between normative and revolutionary periods. The movement of science in normative periods takes place through a "paradigm". Scientific paradigms are accepted patterns in the scientific community for significant periods of time about a major aspect of nature. What makes these patterns valid is the metaphysics or philosophy that governs that paradigm. Therefore, what is "scientific, normative and valid" in one paradigm is "unscientific, abnormal and invalid" in the intellectual, philosophical and cultural context of the other paradigm. Sometimes scientists accidentally encounter phenomena that do not conform to the norms and assumptions governing the paradigm. In the first encounter, these cases are considered as exceptional cases or the product of experimental error, and so on. But when the number of these inconsistencies increases, such justifications no longer work, and the paradigm is in crisis. Over time, this crisis deepens until a new paradigm emerges. As the new paradigm grows, so does the previous critical paradigm. Kuhn calls such a development a "scientific revolution." In his view, the "paradigms" before and after the scientific revolutions are "incomparable."
Kuhn's theory of paradigm is true not only of the history of science, but of all phenomena, including art and literature. In general, it can be said that in each period of time, according to the metaphysics of that period, there is a ruling paradigm that has its own presuppositions, norms and rules. These presuppositions and norms are based upon a fixed pattern that the paradigm as a whole imposes. In these paradigms, only those phenomena (including scientific, artistic, literary, etc.) can emerge that are consistent with the norms and assumptions governing the paradigm, while any innovation will be disregarded.
Accordingly, the imitation of imaginary forms in pre-modern Persian poetry is a phenomenon that should be studied in the presuppositions and norms that dominate the pre-modern paradigm. By examining the premodern paradigm as an all-encompassing whole, one can arrive at assumptions and norms that act as a model for all phenomena of this paradigm. One of these presuppositions is the idea of the originality of the past. In this view, everything in the past has an intrinsic value, so they are only valid and normal when they are imitations of that valuable and sacred past. In the eyes of the pre-modern man, the past is a model of the sacred and golden age, which is always viewed with a respectful eye, and man always remembers it as a dream day. This sacred past is a lost paradise to which all efforts are directed at. 
The manifestation of this presupposition can be seen in all intellectual areas of this paradigm. The originality of the past in the field of history has shown itself in the form of a distant view of time, and in the field of philosophy as a belief in the return of people to the origin of existence (first intellect). Looking at the poetry of Iranian poets from the fifth century AH onwards (until the return period), it is also possible to understand this kind of attitude in the world of literature. These poets have either explicitly mentioned their past poets as the supreme example of poetry, or, without openly praising their past, have accepted them as their role models and tried to write poetry like them. So it is natural that these poets, by following the example of the first Persian poets, instead of depicting their personal poetic experiences, repeat the same imaginary forms and images that had been previously tested by previous poets, and as a result, the imagination in their poetry is imitative and lacks innovation, and even if a poet was innovative, he has not left the realm of vision and attitude of the ancients.