Under the rude Tartar invaders of Persia, who could have no sympathy with independent thought, there could be no progress of ideas. Ṣūfīism, owing to its association with religion, went on systematising old and evolving new ideas. But philosophy proper was distasteful to the Tartar. Even the development of Islamic law suffered a check; since the Ḥanafite law was the acme of human reason to the Tartar, and further subtleties of legal interpretation were disagreeable to his brain. Old schools of thought lost their solidarity, and many thinkers left their native country to find more favourable conditions elsewhere. In the 16{th} century we find Persian Aristotelians--Dastūr Isfahānī, Hīr Bud, Munīr, and Kāmrān--travelling in India, where the Emperor Akbar was drawing upon Zoroastrianism to form a new faith for himself and his courtiers, who were mostly Persians. No great thinker, however, appeared in Persia until the 17{th} century, when the acute Mulla Ṣadra of S̱ẖīrāz upheld his philosophical system with all the vigour of his powerful logic. With Mulla Ṣadra Reality is all things yet is none of them, and true knowledge consists in the identity of the subject and the object. De Gobineau thinks that the philosophy of Ṣadra is a mere revival of Avicennaism. He, however, ignores the fact that Mulla Ṣadra's doctrine of the identity of subject and object constitutes the final step which the Persian intellect took towards complete monism. It is moreover the Philosophy of Ṣadra which is the source of the metaphysics of early Bābism. But the movement towards Platonism is best illustrated in Mulla Hādī of Sabzwār who flourished in the 18{th} century, and is believed by his countrymen to be the greatest of modern Persian thinkers. As a specimen of comparatively recent Persian speculation, I may briefly notice here the views of this great thinker, as set forth in his Asrār al-Ḥikam (published in Persia). A glance at his philosophical teaching reveals three fundamental conceptions which are indissolubly associated with the Post-Islamic Persian thought:-- 1. The idea of the Absolute Unity of the Real which is described as "Light". 2. The idea of evolution which is dimly visible in Zoroaster's doctrine of the destiny of the human soul, and receives further expansion and systematisation by Persian Neo-Platonists and Ṣūfī thinkers. 3. The idea of a medium between the Absolute Real and the Not-real.