Sarvastivada teachings—which were criticized by Nāgārjuna—were reformulated by scholars such as Vasubandhu and Asanga and were adapted into the Yogacara school. While the Mādhyamaka school held that asserting the existence or non-existence of any ultimately real thing was inappropriate, some exponents of Yogacara asserted that the mind and only the mind is ultimately real (a doctrine known as cittamatra). Not all Yogacarins asserted that mind was truly existent; Vasubandhu and Asanga in particular did not.[web 11] These two schools of thought, in opposition or synthesis, form the basis of subsequent Mahayana metaphysics in the Indo-Tibetan tradition.