semantic studding in Mulla Sadra’s works, the concept of faith has a vast network relation to other concepts. One of the most important concepts is knowledge. Mulla has divided the knowledge to legal and rational, adventitious and hereditary, and apocalyptic and the transactional forms. In his view, the real knowledge is the legal rational, hereditary and apocalyptic knowledge. This knowledge has been considered equivalent of faith in many positions in Mulla Sadra works. He has advanced traditional, rational and literal evidences for this claim. However, in his statement we can see sometimes that the knowledge is regarded as a condition of faith and sometimes as its part. Sometimes faith is the condition of the knowledge and sometimes they are quite opposite of each other. Some believe that the cognition different from the knowledge, but Mulla Sadra regards it as equivalent of the knowledge. Thus, the concepts of disbelief and ignorance are used in his works as opposite of the faith. The infidelity is sometimes equivalent of ignorance and sometimes is its toughest degree. This conceptual network can be explained according to the view of Mulla Sadra about the role of intellectual faculty in faith. The strengths of intellectuality is the cause of the faith, knowledge and cognition, and the weakness of intellectuality is the cause of ignorance and unbelief. In his view, other human faculties such as faculty of estimation have also some role in faith and unbelief.