Moreover...

Moreover, it is believed that the reality of matter is one, while the phenomena that manifest themselves in consciousness are fundamentally various. The data of the senses smells, tactual impressions, impressions of taste, sounds, colours are fundamentally of a different nature from one another. Further, perceived impressions of each class are different from imagined, dreamt, or recalled impressions of that class. Again, all the impressions of the senses are fundamentally different from thoughts.

None of them can be imagined as being reducible into another, nor all of them can be reducible to any single substratum called matter. Furthermore, each of the impressions of the senses, and so also thoughts, are fundamental realities experienced by the mind. They are signs and images in that they represent something other than themselves, but in themselves they are things in that they are what they are.

Material objects are represented by them in that they are images; but nothing that we know about matter enters their actual constitution as things. Now, going back to al-Sadr's discourse, if there are two sides to a human being, one spiritual or immaterial and the other material and physical, how do the two sides constantly affect each other? Plato was unable to bridge the gulf between the soul and the body.

Descartes' theory of parallelism denied that there was any causal relation between physical and mental events, and hence admitted an unbridgeable gulf between the body and the mind. This failure leads to the crystallization of the inclination in European philosophy to explain man's being on the basis of one principle, matter or mind, leading to the opposite tendencies of materialism and idealism.

In the Islamic world, the explanation of human being on the basis of two principles, spiritual and material, found its most convincing formulation in the thought of Sadr al-Muta'allihin or Mulla Sadra. According to Mulla Sadra, movement does not occur only in the accidents, but goes on in the substances and in the core of the being of things. He called it al-harakat al-jawhariyyah, substantial movement.

According to his theory, matter in its substantial movement pursues the completing of its existence until it assumes an immaterial being, becoming free from all materiality. Thus, there remains no dividing line between spirituality and materiality. Rather, they are two levels of existence.