The scholar Walpola Rahula explains that once Ananda the attendant asked Gautama Buddha, "People say the word Sunya. What is Sunya?" The Buddha replied, "Ananda, there is no self, nor anything pertaining to self in this world. Therefore, the world is empty." This idea influenced Nagarjuna's philosophy when he wrote the text, Madhyamika Karika. Related to the concept of Sunyata is the notion of the store-consciousness in Mahayana Buddhism which has its seed in the Theravada texts. The Mahayana philosophers have developed it into a deep psychology and philosophy.