Sadr al-Din al-Shirazi (Mulla Sadra) is perhaps the single most important and influential philosopher in the Muslim world in the last four hundred years. The author of over forty works, he was the culminating figure of the major revival of philosophy in Iran in the sixteenth and seventeenth centuries. Devoting himself almost exclusively to metaphysics, he constructed a critical philosophy which brought together Peripatetic, Illuminationist and gnostic philosophy along with Shi'ite theology within the compass of what he termed a 'metaphilosophy', the source of which lay in the Islamic revelation and the mystical experience of reality as existence.

Mulla Sadra's metaphilosophy was based on existence as the sole constituent of reality, and rejected any role for quiddities or essences in the external world. Existence was for him at once a single unity and an internally articulated dynamic process, the unique source of both unity and diversity. From this fundamental starting point, Mulla Sadra was able to find original solutions to many of the logical, metaphysical and theological difficulties which he had inherited from his predecessors. His major philosophical work is the Asfar (The Four Journeys), which runs to nine volumes in the present printed edition and is a complete presentation of his philosophical ideas.