 Advaita is one of the six most known Hindu philosophical systems and literally means "non-duality".Its first great consolidator was Adi Shankaracharya, who continued the work of some of the Upanishadic teachers, and that of his teacher's teacher Gaudapada.By using various arguments, such as the analysis of the three states of experience—wakefulness, dream, and deep sleep, he established the singular reality of Brahman, in which Brahman, the universe and the Atman or the Self, were one and the same.