The Buddha did not speculate about the ultimate nature of reality, being concerned with the more urgent matter of the relief of suffering. It is the members of the Theravada school of Buddhism, who take up this matter somewhat. Even if disinclined to speculation in certain areas, the Theravada tradition nevertheless involves a complex philosophy of its own, exemplified in the work of Buddhaghosa.
However a system addressing issues ignored by the Buddha emerged with the second major school of Buddhism, the Mahayana, which had a major impact in Tibet, China and Japan. If enlightenment is direct awareness of reality, then it is difficult to resist the urge to say something about what this reality might be. Two leading points of view developed on this question, each associated with a great philosopher in the Indian Buddhist tradition. They are the Madhyamika tradition of Nagarjuna and the Yogacara tradition associated with Vasubandhu. For Nagarjuna, ultimate reality can be described only as a Void (Sanskrit: Sunyata, i.e. is not properly characterizable in conceptual terms), while for Vasubandhu it can be said to be mental in nature, and he gives a detailed account of different types of consciousness.