Dicuss al-biruni's understanding of the caste …

Al biruni spent years in the company of brahmana priests and scholars, learning sanskrit and studying religious and philosophical texts.
Al biruni tried to explain the caste system by looking for parallels in other societies.
In ancient persia, four social cateogaries were recognised. Thus, he attempted to suggest that social divisions were not unique to India.
But at the same time, he pointed out that within islam, all men were equal, differing only i their observance of piety.
Al biruni diapproved of the notion of pollution practised in the varna system. He remarked that everything which falls in a state of impurity, strives and succeeds in attaining its original condition of purity. henceforth, the notion of social pollution, intrinsic to the varna system was contrary to the laws of nature.