Substance.

‎'I am a part of the part that at first was all, part of the darkness that gave birth to light, that supercilious light which now disputes with Mother Night her ancient rank and space, and yet can not succeed; no matter how it struggles, it sticks to matter and can't get free. Light flows from substance, makes it beautiful; solids can check its path, so I hope it won't be long till light and the world's stuff are destroyed together.'

- Taken from the speech by Mephistopheles in Goethe’s Faust.