Adi Shankara's works deal with logically establishing the doctrine of Advaita Vedanta as he saw it in the Upanishads. He formulates the doctrine of Advaita Vedanta by validating his arguments on the basis of quotations from the Vedas and other Hindu scriptures. He gives a high priority to swanubhava ("personal experience") of the student. His works are largely polemical in nature. He directs his polemics mostly against the Sankhya, Buddha, Jaina, Vaisheshika and other non-vedantic Hindu philosophies. Traditionally, his works are classified under Bhasya ("commentary"), Prakarana grantha ("philosophical treatise") and Stotra ("devotional hymn"). The commentaries serve to provide a consistent interpretation of the scriptural texts from the perspective of Advaita Vedanta. The philosophical treatises provide various methodologies to the student to understand the doctrine. The devotional hymns are rich in poetry and piety, serving to highlight the relationship between the devotee and the deity. Adi Shankara wrote Bhashyas on the ten major Upanishads, the Brahma Sutras and the Bhagavad Gita. In his works, he quotes from Shveshvatara, Kaushitakai, Mahanarayana and Jabala Upanishads, among others. Bhashyas on Kaushitaki, Nrisimhatapani and Shveshvatara Upanishads are extant but the authenticity is doubtful.[53] Adi Shankara's is the earliest extant commentary on the Brahma Sutras. However, he mentions older commentaries like those of Dravida, Bhartrprapancha and others.