According to a doctrine widely held by most medieval philosophers and theologians, whether in the Muslim or Christian world,
there are no metaphysical distinctions in God whatsoever. As a result of the compendious theorizing that has been done on
this issue, the doctrine, usually called the doctrine of divine simplicity, has been bestowed a prominent status in both Islamic and Christian philosophical theology. In Islamic philosophy some well-known
philosophers, such as Ibn Sina (980–1037) and Mulla Sadra (1571–1640), developed this doctrine through a metaphysical approach.
In this paper, considering the historical order, I shall first concentrate on Ibn Sina’s view. Then I shall turn to the theory
of divine simplicity of Thomas Aquinas (1225?–1274), as the most developed and comprehensive version of the medieval theories
in Christian world. Finally, I will return to Islamic philosophy and explore the more complicated and mature account of the
doctrine as it was introduced by Mulla Sadra according to his own philosophical principles.