For al-Attas, Islamic metaphysics is a unified system that discloses the ultimate nature of Reality in positive terms, integrating reason and experience with other higher orders in the suprarational and transempirical levels of human consciousness. He sees this from the perspective of philosophical Sufism. Al-Attas also says that the Essentialist and the Existentialists schools of the Islamic tradition address the nature of reality. The first is represented by philosophers and theologians, and the latter by Sufis. The Essentialists cling to the principle of "mahiyyah" (quiddity), whereas the Existentialists are rooted in "wujud" (the fundamental reality of existence) which is direct intuitive experience, not merely based on rational analysis or discursive reasoning. This has undoubtedly led philosophical and scientific speculations to be preoccupied with things and their essences at the expense of existence itself, thereby making the study of nature an end in itself. Al-Attas maintains that in the extra-mental reality, it is "wujud" (Existence) that is the real "essences" of things and that what is conceptually posited as mahiyyah ("essences" or "quiddities") are in reality accidents of existence.