Metaphysical Form in Ancient and Medieval Thought

This question, and many others, received a balanced "naturalistic" answer in the Aristotelian Christian synthesis of St. Thomas Aquinas (c. 1224–1274), reconciling Christian religious doctrine and important elements of the Neoplatonic tradition with Aristotelian philosophy. For Aquinas, divine grace does not work against nature (even if it could), but through nature: gratia non tollit naturam, sed perficit—grace does not destroy nature, but perfects it (2SN, d. 9, q. 1, obj. 8; ST1, q. 1, a. 8, resp. 2.). Therefore, the divine light of Augustinian illumination for Aquinas becomes the same as the Aristotelian active intellect, which (pace Averroës) is not a separate substance, but a natural, although immaterial, power of the human soul. The soul itself is the Aristotelian substantial form of the human body, which, however, on account of its immaterial power, is naturally capable of surviving the death of a human person, to be supernaturally resurrected in the same body by God. The human soul thus straddles the ontological divide between material and immaterial, having access to both. The natural world of material substances, each having its natural powers on account of its characteristic substantial form, but all in need of a constant influx of energy for its natural operation, is kept in motion by the movement of heavenly spheres, in accordance with the laws of Aristotelian physics. These in turn are moved by their immaterial movers, Aristotle's subsistent forms or separate substances, which Aquinas further identifies with biblical angels. But even these immaterial forms are not pure actuality or energy (actualitas, Lat.; energeia, Gr.). Therefore, they owe their activity as well as their actual being to the Aristotelian Prime Mover, the first cause of all causes, which for Aquinas is also the creator of the universe, both material and immaterial, namely, the Judeo-Christian God, the subsistent form that is pure energy or actuality, that is, nothing but pure being: He Who Is (ST1, q. 13, a. 11; Exodus 3:14).