There are so many definitions for the reason and the spirit in both Islamic philosophy and old and new Western philosophies that one is reminded of the story of the elephant in darkness. Therefore, a study of the relationships between them will give rise to some questions and problems. It seems that more research is required concerning the relation between the spirit and reason, which has mainly been defined as wisdom, a faculty, or a predisposition, particularly in terms of the perfection of intellectus materialis. The present paper mainly deals with the quality of the reason-spirit relation, specifically concerning the role of the trans-substantial motion (Mulla Sadra's theory) in the above perfection.