Aquinas on Intelligent Extra-Terrestrial Life

The Thomist 65 (2001): 239-58 AQUINAS ON INTELLIGENT EXTRA-TERRESTRIAL LIFE MARIE I. GEORGE St. John's University Jamaica, New York Both as a philosopher and as a theologian, Aquinas took an interest in the question of whether there are intelligent material beings other than humans in the universe. As a philosopher he sought to understand the order of the universe, which entails ascertaining what beings are in the universe. As a theologian he sought knowledge of created beings insofar as it leads to a greater understanding, admiration, and love of the creator, and also insofar as it frees one from superstitious beliefs that pose an obstacle to faith in God.1 Although Aquinas was unable to approach the question of the existence of intelligent extra-terrestrial life from the scientific perspective of our day, he does raise some generally overlooked philosophical questions regarding such beings. His theological reflections are helpful for addressing the popular claim that the discovery of intelligent extraterrestrial life would spell the end of Christianity. Aquinas's position is that it is possible that ETs2 of a certain sort exist, but improbable that they do. I will consider first Aquinas's philosophical positions on the possibility of ET life, then his theological views thereon, and dose with his arguments regarding the probability of ET life. 1 Cf. Summa contra Gentiles, ed. C. Pera, 0.P., et al. (Turin: Marietti, 1961),II, cc. land 3. 2 Henceforth ET will be used as an adjective in place of "intelligent extra-terrestrial" and will also be used as a noun to name beings of this sort. 239 240 MARIE I. GEORGE I. THE POSSIBILilY OF ET LIFE When people today think ofextra-terrestrial life they generally imagine another earth-like planet inhabited by beings with odd-looking faces who are brainier than ourselves. Aquinas never considers ETs as inhabitants of another earth-like planet. This is because he thinks that there cannot be a more than one world like ours.3 His views on the material composition of the universe further restrict what he considers possible as far as ET life is concerned. He thinks that celestial bodies are made of a single incorruptible element, while the earth is the only place where corruptible elements are found. Thus, his only candidate for ETs is the celestial bodies themselves, which some philosophers thought might be animate. He does, however, consider the possibility of the existence of beings other than humans that are composed of the earthly elements. Though he would necessarily imagine them as dwelling on the earth, we may take his arguments as applicable to the possibility of their existence on another planet. The arguments against an intellectual substance being united to a single element are straightforward: If some intellectual substance is united to one of the simple bodies [corruptible elements] as form, either this being will have intellect alone or it will have other powers such as those which pertain to the sensitive or nutritive part as is the case in man. If, however, it has intellect alone, it would be vain for it to be united to the body. For every form of a body has some proper operation through the body. The intellect however does not have some operation belonging to the body except according as it moves the body.... The motions of the elements are from natural movers, namely, from the things which generate them, and they do not move themselves; whence there is no need as far as their motion is concerned for them to be animate. If on the other hand the intellet."tUal substance which is supposed to be united to an element or part of it has other parts of the soul [in addition to intellect], it will be necessary to find in a simple body a diversity of organs; which is incompatible with the .i Cf. In Libros Aristotelis De Caelo et Mundo, Leonine ed. (Rome: Society for the Propagation of the Faith, 1886), I, c. 9, lect. 19. Cf. also Summa Theologiae I, q. 47, a. 3. AQUINAS ON EXTRA-TERRESTRIAL LIFE 241 body's simplicity. Therefore, an intellectual substance cannot be united as form to some element...