<P> Aristotle argued at length against many aspects of Plato's forms, creating his own doctrine of hylomorphism wherein form and matter coexist . Ultimately however, Aristotle's aim was to perfect a theory of forms, rather than to reject it . Although Aristotle strongly rejected the independent existence Plato attributed to forms, his metaphysics do agree with Plato's a priori considerations quite often . For example, Aristotle argues that changeless, eternal substantial form is necessarily immaterial . Because matter provides a stable substratum for a change in form, matter always has the potential to change . Thus, if given an eternity in which to do so, it will, necessarily, exercise that potential . </P> <P> Part of Aristotle's psychology, the study of the soul, is his account of the ability of humans to reason and the ability of animals to perceive . In both cases, perfect copies of forms are acquired, either by direct impression of environmental forms, in the case of perception, or else by virtue of contemplation, understanding and recollection . He believed the mind can literally assume any form being contemplated or experienced, and it was unique in its ability to become a blank slate, having no essential form . As thoughts of earth are not heavy, any more than thoughts of fire are causally efficient, they provide an immaterial complement for the formless mind . </P> <P> In the philosophical school of Neoplatonism, most active in Late Antiquity, claimed that the physical and the spiritual are both emanations of the One . Neoplatonism exerted a considerable influence on Christianity, as did the philosophy of Aristotle via scholasticism . </P> <P> In the scholastic tradition of Saint Thomas Aquinas, a number of whose doctrines have been incorporated into Roman Catholic dogma, the soul is the substantial form of a human being . Aquinas held the Quaestiones disputate de anima, or "Disputed questions on the soul", at the Roman studium provinciale of the Dominican Order at Santa Sabina, the forerunner of the Pontifical University of Saint Thomas Aquinas, Angelicum during the academic year 1265 - 66 . By 1268 Aquinas had written at least the first book of the Sententia Libri De anima, Aquinas' commentary on Aristotle's De anima, the translation of which from the Greek was completed by Aquinas' Dominican associate at Viterbo William of Moerbeke in 1267 . Like Aristotle, Aquinas held that the human being was a unified composite substance of two substantial principles: form and matter . The soul is the substantial form and so the first actuality of a material organic body with the potentiality for life . While Aquinas defended the unity of human nature as a composite substance constituted by these two inextricable principles of form and matter, he also argued for the incorruptibility of the intellectual soul, in contrast to the corruptibility of the vegetative and sensitive animation of plants and animals . His argument for the subsistence and incorruptibility of the intellectual soul takes its point of departure from the metaphysical principle that operation follows upon being (agiture sequitur esse), i.e., the activity of a thing reveals the mode of being and existence it depends upon . Since the intellectual soul exercises its own per se intellectual operations without employing material faculties, i.e. intellectual operations are immaterial, the intellect itself and the intellectual soul, must likewise be immaterial and so incorruptible . Even though the intellectual soul of man is able to subsist upon the death of the human being, Aquinas does not hold that the human person is able to remain integrated at death . The separated intellectual soul is neither a man nor a human person . The intellectual soul by itself is not a human person (i.e., an individual supposit of a rational nature). Hence, Aquinas held that "soul of St. Peter pray for us" would be more appropriate than "St. Peter pray for us", because all things connected with his person, including memories, ended with his corporeal life . </P>

Who argued that while the experience of a split second