In On Corporeal Motion and Light, Grosseteste identifies nature, conceived by Aristotle as an internal source of motion and rest, with the first form, light, and claims that all kinds of corporeal change are the "multiplicative force" of the first corporeal form, light (Baur 1912, 92).
He sets out this theory most fully in On Light, but elements of it are present also in his commentaries on the Posterior Analytics and Physics, in On Corporeal Change and Light, and in his commentary on Ecclesiasticus 43: 1–5, also known as On the Operations of the Sun.
See Kant's formulation of his first "law of mechanics" in the Metaphysical Foundations (4, 541; 80 81): "In all changes of corporeal nature the total quantity of matter remains the same, neither increased nor diminished".
It is distinguished as a principle of actuality in a being from the material principle which is a principle of potentiality and change in corporeal beings.
Each of them governs a separate sphere of reality, eternity the intelligible being, time the temporal (corporeal and psychic) world of change.
Moreover, if an incorporeal being were to act directly on a corporeal one, it too would be changed (by becoming a cause or a moved mover), which is unthinkable given the unchangeable nature of incorporeal entities.
It is called "everlastingness" (sarmad) when related to God and the Intelligences (angels) that are permanent and do not move or change in any way, "eternity" (dahr) when related to the totality of the world of movement and change, and "time" (zamān) when related to corporeal beings that make up the world of movement and change.
Regarding BPM, it is necessary that there be one matter that is the substrate of substantial change, and this matter is the corporeal substance, that is, substance plus the form of corporeity (DOS 244 245).
If it is not corporeal, it is not subject to division or change.
Everything spiritual presses toward corporealization; its eternal figure is a corporeal figure.
