De Luce seu de Inchoatione Formarum (c. 1215-1220)
Context: The first corporeal form, which some call corporeity, I hold to be light. For light of its own nature diffuses itself in all directions, so that from a point of light a sphere of light of any size may be instantly generated, provided an opaque body does not get in the way. Corporeity is what necessarily follows the extension of matter in three dimensions, since each of these, that is corporeity and matter, is a substance simple in itself and lacking all dimensions. But simple form in itself and in dimension lacking matter and dimension, it was impossible for it to become extended in every direction except by multiplying itself and suddenly diffusing itself in every direction and in its diffusion extending matter; since it is not possible for form to do without matter because it is not separable, nor can matter itself be purged of form. And, in fact, it is light, I suggest, of which this operation is part of the nature, namely, to multiply itself and instantaneously diffuse itself in every direction. Therefore, whatever it is that produces this operation is either light itself or something that produces this operation in so far as it participates in light, which produces it by its own nature. Corporeity is therefore either this light, or is what produces the operation in question and produces dimensions in matter in so far as it participates in this light itself and acts by virtue of this same light. But for the first form to produce dimensions in matter by virtue of a subsequent form is impossible. Therefore light is not the form succeeding this corporeity, but is this corporeity itself.
