The issue of science and rationalism (knowledge and cognition) achievement in humans has always been present in the mind of philosophers and scientists. A mong the old philosophers, Sheikh Shahabedin Yahya Sohravardi paid special attention to these issues and in his many different Persian and Arabic philosophical publications, he presented different definitions of this subject.
The goal of this study is to answer this question that whether these different definitions are due to lack of understanding or mental depression of Sheikh in this area or indicating his gradual thought evolution. Answering to this question depends on precise investigation of these definitions and comparing them with each other and determining their chronological delay or priority.
Results of this study show that, because Sheikh-Eshragh was under the influence Massa? philosophy in his early works, he concluded that science and rationalism result from the form of objects in mind. Then, in the process of his thought evolution he presented different descriptions of this issue. Finally, after his experience in Nori-Eshraghi, he concluded that science and rationalism are the result of brilliant personality.
The sources used in this paper are, firstly, Persian and Arabic philosophical works that were accessible to Sheikh and two famous and authentic commentaries by Shahrzori and Ghotbedin Shirazi about Hekmatol-Eshragh. The reason of this is to use Sheikh’s sayings or famous commentator of Hekmatol-Eshragh directly, Other available sources are also used for this study. Since Mola-Sadra was influenced by Sheikh-Eshragh a lot, the differences of Mola-Sadra’s views and Sheikh’s views about this issue are also investigated.