 Kilwardby’s theory is, however, not absolutely original, as scholars (in particular Weisheipl) have shown. In fact, some sixty years earlier, John Blund argued for the same explanation in his Tractaus de anima (paragraph 10); here he stated that heaven (including all celestial spheres) is moved by nature and not by the soul or celestial beings. This view seemed to go unnoticed until Kilwardby referred to it; originality claims apart, the significance of Kilwardby’s statement must be emphasized. The interest of his solution is in how it harmonizes a natural explanation for the phenomenon of celestial motion – designating the instinct of their [the celestial bodies’] own weight as its cause – while at the same time it safeguards God’s influence in the natural world: God is not the direct mover, but the one who endows these bodies with their instinct (D43Q 2, 14; see Silva 2007 for references).