'Do you think that he who does not live, can perceive and feel? It cannot be. It results then, that the soul lives ever.... 'Nor has it power to exercise sense, unless it lives. Therefore the soul always lives.'
At the time of physical death, Augustine confirms that 'the soul may be conducted out of the body unharmed, and guided to a place where it cannot be extinguished.'
Science is eternal for Augustine - for what exists and is unchangeable must be eternal. Nothing in which an eternal thing exists, can be non-eternal or mortal. When we reason it cannot be the body, as when the mind thinks in contrast to bodily desires and needs it can turn away and reject them. He agues that nothing pertaining to the body is eternal, therefore cannot help the eternal mind, striving to understand beyond time and material. Without science, one simply cannot reason, for thought is 'right reasoning moving from the certain to the investigation of the uncertain.' Science is the knowledge of all things; and this proves, for Augustine, that the human mind and soul always lives.
Over the course of his writings, Augustine does make a slight, yet important change to his views on the soul. Initially, the emphasis is on reason, and the soul ruling the human body. However, latterly, he places more importance on the unity of the body and soul; believing that the human being consists of a rational soul, controlling the body. He writes, the 'soul which has a body does not make two persons, but one human being.' Therefore there is a clear understanding of psychosomatic unity. He does continuously remain true to his platonic understanding of forms, where abstract ideas reside. There is evidently a clear distinction between material and immaterial substances; body and soul.
Thomas Aquinas, held similar views regarding the separable body and soul; material and immaterial. He does however take an Aristotelian viewpoint,with the idea of the soul being able to be abstractly separate from the body. For Aquinas, one argument in favour of the soul's immortality is the fact we can think abstractly about ideas out-with or beyond material substances around us. This is, for him, evidence of the soul being able to exist without attachment to the material world. Aquinas argues that the soul, being a spiritual and immaterial entity, does not depend on matter and can exist separately from the body. He believes that human existence, in its perfect and ideal form, is in the dual nature of body and soul which relates to his belief in the resurrection.
To conclude, although Aquinas discusses the sole from a different (Aristotelian) perspective, he certainly uses Augustinian theology in order to argue for the immortality and vitalness of the God-given soul. He offers Saint Augustine's understanding of the soul's nature, as 'the first principle of life of those things which live: for we call living things animate and those things which have no life, inanimate.'
Melanie Dorn, Augustine v Aquinas, in 'atanystreetcorner.wordpress.com.'
Aquinas, Summa Theologica, First Part Questions 75-76.
Augustine, Soliloquies, Book II.