The concept of God in Hinduism varies in its diverse traditions. Hinduism spans a wide range of beliefs such as henotheism, monotheism, polytheism, panentheism, pantheism, pandeism, monism, atheism and nontheism. Forms of theism find mention in the Bhagavad Gita. Emotional or loving devotion (bhakti) to a primary god such as avatars of Vishnu (Krishna for example), Shiva and Devi emerged in the early medieval period, and is now known as Bhakti movement. Other Hindus consider atman within every living being to be same as Vishnu or Shiva or Devi, or alternatively identical to the eternal metaphysical Absolute called (Brahman) in Hinduism. Such a philosophical system of Advaita or non-dualism as it developed in the Vedanta school of Hindu philosophy, especially as set out in the Upanishads and popularised by Adi Shankara in the 9th century has been influential on Hinduism.