Existence and knowledge are the two main fields argued in the Islamic philosophy; In this field, subjects such as: knowledge, union of intellect and intelligible and manifestations of existence are argued. The existence of the knowledge is an external one which can be found apart from our mind in the real world. As it can also be detected by human intelligence, it is also known as a mental connotation and, as a result of this, the nature of knowledge can be detected and known. Because of the effects of the knowledge, mental-existence can be known which can be led to the acknowledgement of the knowledge essence. Mulla Sadra believes that knowledge is just a mode of existence, for, God' s acknowledgement to his own existence and to the objects and also direct and independent ideas is not the result of our sense- dependent mind. So our knowledge about objects, our understandings and conceptions are obtained by our sensual activities in the relationship with the outer phenomena. So, our mind, in its inner evolution, can relate and visualize the meanings in the imaginal world, in its inner evolutional manner. This sort of connection can be obtained by sense-independent intermediate world.The secret of our mental direct discoveries, physical ascensions and hereafter associations are related to this kind of sense-independent knowledge. Intellectual conceptions are subordinate of sense- independent ideas and are not visualized in our mind. Our mind while relating to the sense- independent world is also united with the sense-independent intellect and the lightening world, and as a result of this union, it can visualize total senseindependent ideas.