Wilber's understanding of the levels of consciousness, or reality, ranging from matter to body to mind to soul to spirit, or from prepersonal to personal to transpersonal, is often referred to as the "Great Chain of Being". This overarching framework, that is adapted from the "perennial philosophy" of the worlds great spiritual traditions, is later reformulated by Wilber as the "Great Nest of Being". That is, not just a simple linear hierarchy, but a kind of nested hierarchy, or holarchy. Human development, and evolution, is considered to move up this holarchy.