  Bonaventure discounts the possibility that light is a substance, because it is purely active and if it were a substance in its own right it would be God and not a creature. He does allow, however, that light is a substantial form and is the substantial form that is concomitant with the mass of matter in its primordial  state.[26]  In this originating condition, light gave the mass of matter its extension and visibility and the hierarchy of heavenly bodies corresponds to the hierarchy of things capable of partaking either more or less in the light that renders bodies active and extended. For Bonaventure, then, light is a substantial form, but only the partial perfection of any given physical substance, whether celestial or terrestrial. Since Bonaventure endorses, usually without any elaborate argumentation, the general claim that there is a plurality of substantial forms within any composite thing, his doctrine of light really means that light is the first form, endowing each thing with extension, and preparing the way for further perfections such as the forms of the elements or the forms of mixtures or compounds.