 Things belonging to the latter class continue to exist after their causes perish—for instance, a house continues to exist after the death of its builder. By contrast, things belonging to the former class perish as soon as motion ceases—for instance wind does not continue to exist as soon as the motion of air ceases (Tiqqun 30: 30; cf. Averroes Tahāfut al-Tahāfut, fourth discussion: 156–8). These things are said to be more in need of a cause than things belonging to the former class are, for should the cause disappear from existence “for a twinkling of an eye”, they would necessarily perish (Tiqqun n.30: 30). The universe as a whole belongs to this class. Both the natural and celestial realms subsist because their constituent “parts are eternally originated” through the motion produced by the Prime Mover; the parts of the natural and celestial realms referring to sublunary existents and the “successive” stages of celestial motion respectively (Tiqqun, n.30: 30). 