Your complimentary articles

You’ve read one of your four complimentary articles for this month.

You can read four articles free per month. To have complete access to the thousands of philosophy articles on this site, please

SUBSCRIBE NOW

Articles

Thomas Aquinas on Extraterrestrial Life

Babatunde Onabajo tells us why Aquinas did not believe in aliens.

The belief that life exists outside of Earth is known as ‘cosmic pluralism’. Intriguingly, this was briefly a topic of discussion during the medieval period, in the works of none other than St Thomas Aquinas.

Thomas Aquinas (1224-74) was a Roman Catholic friar, priest, theologian, and philosopher. His writings left a huge impact on the thought of the Catholic church – so much so that they still hold sway even to the present day. It is difficult, maybe even impossible, to navigate the extensive body of Catholic theology without coming across his name. He also wrote extensive commentaries on the work of Aristotle – so much so that the saying was used in the Middle Ages, ‘Without Thomas, Aristotle is mute’.

Aquinas’s most famous book is the Summa Theologica (1265). It addresses a wide range of philosophical and theological questions, ranging from whether angels exist, through what is pride, through to the source of human laws. The Summa is notoriously large, and is divided into five parts: First Part, First Part of the Second Part, Second Part of the Second Part, Third Part, and Supplement to the Third Part! It should be noted however that the Supplement to the Third Part was not written by St Thomas himself, as he was unable to complete the work due to inconveniently dying; rather, it was compiled by a friend based on a commentary Aquinas had made of another influential theologian, Peter Lombard (sometimes called the ‘Master of Sentences’). The format of Aquinas’s Summa, and indeed, of several of his writings, would strike many readers today as rather odd. It is presented in the form, first, of a question, followed by several arguments in response to that question, followed by St Thomas disputing or responding to said arguments. This though was the format of many medieval writings. A rough parallel today might be submissions made to a court between two or more disputing parties.

Arguments For Aliens

Although this is not remembered or spoken about much today, Aquinas also addressed the question of whether or not life exists outside of Earth. The discussion is in the First Part, and is under Question 47 Art.3, titled, ‘Whether there is only one world?’.

Three arguments are presented in favour of life existing outside of Earth, before Aquinas explains why he believes these arguments are incorrect.

The first argument is that God’s power is infinite, or in theological terms, that God is omnipotent. Therefore, if God could create one world, he could create multiple worlds. There is therefore no reason why there are not multiple ‘Earths’ in the universe. Although we live in a much more secular age than that experienced by Aquinas, this line of thought sometimes still appears in those with religious leanings who believe in life beyond Earth.

The second argument presented is that of quantity: life on Earth is inherently good, and so because God is good, it stands to reason that God would create multiple worlds as opposed to just one, to multiply the goodness. The nature of goodness is, after all, to spread goodness: as we say in our day, ‘sharing is caring’; or in the words of Jesus, ‘no one hides a lamp under a basket’.

The third argument is arguably the most abstract, but it basically states that because the world is made of matter, there is nothing stopping multiple worlds from existing, just as there is nothing stopping multiple men from existing.

Aquinas Responds

Aquinas addresses all of these points characteristically, by first turning to sacred scripture. In his Gospel, John states: “He was in the world, and the world was made through him, yet the world did not know him” (John 1:10). From this Aquinas argues that this means that life only exists on Earth and not elsewhere – otherwise the Gospels would have used the plural rather than the singular of ‘world’. Aquinas then proceeds to lays out his beliefs as to why life only exists on Earth, before addressing each argument above in turn.

He begins by arguing that life only exists on Earth because, just as there is only one God – after all, Christianity is a monotheistic religion – it stands to reason that all things are ordained for one purpose (that is, God’s purpose); and just as all things are ordained for one purpose, there is only one world on which that purpose is being fulfilled – namely, Earth. (Aristotle’s influence is apparent here, as Aristotle was vocal in his belief in telos or purpose, which is his fourth type of cause.) Aquinas’s next words are most prescient: “Therefore those only can assert that many worlds exist who do not acknowledge any ordaining wisdom, but rather believe in chance, as Democritus, who said that this world, besides an infinite number of other worlds, was made from a casual concourse of atoms.” These words citing the Greek philosopher Democritus, who was a Stoic and an adherent of atomism, are prescient, because they present the viewpoint of those in the modern world who believe that life exists outside of Earth. Many say today, “Given the number of stars and planets in the universe, intelligent life elsewhere must surely exist.” Since 1965 we’ve even had an equation to estimate the number (N) of technologically-advanced civilizations in our Milky Way galaxy. This is the Drake equation, named after astrophysicist Frank Drake, who died only in 2022: N = R_* f_p n_e f_l f_i f_c L.

The values of some of these variables are now known, but for others we have only guesses. If any of them have a true value that is very small, then N could plausibly just be one (ie, us). In any case, Aquinas believes this generalisation to life around the universe is fallacious, as humanity did not arise from chance, but from the working of a higher purpose, namely, the purpose of God.

Aquinas then responds to the first argument, that an all-powerful God can create as many worlds as he likes, by relying on both Plato and Aristotle to say that many worlds (‘Earths’) would contradict there being a specific end or goal to life. Since there is only one end or one purpose, there can only be one Earth.

Aquinas makes a related response to the second argument, that the goodness of God must be multiply expressed, since it’s better for many good things to exist than just one. Aquinas argues that if this line of thought were to follow, then there would potentially be an infinite number of worlds existing in the universe, given that God’s power is infinite, but that again, this contradicts the essence of there being just one end or purpose for the world.

Aquinas responds to the third argument by saying that the world (the universe?) is composed of the whole of its matter. Therefore if there were earths other than this one, every earth would naturally be carried to (gravitate to?) this central one. Not a bad argument for the 13th century, though it is fair to say that our understanding of celestial mechanics has improved since then.

Where Is Everyone?

Estimates suggest that there are at least a hundred billion stars, and as many planets, in the Milky Way alone, let alone in other galaxies. Despite this, outer space seems eerily quiet – so much so that the Italian-American physicist Enrico Fermi (1901-54) once asked, “But where is everybody?”

‘Where are all the aliens?’ is a puzzle astrophysicists have so far failed to adequately answer. Yet whilst the modern Catholic Church has a more neutral view on whether or not life exists beyond Earth, Aquinas was forthright: he argued that space is, in fact, desolate, and that Earth and humanity have a special place and purpose in God’s scheme of things.

Given that no clear evidence to date has established that there is in fact any life beyond Earth, St Thomas Aquinas has yet to be proven wrong.

Babatunde Onabajo is the Director of ChurchMapped Limited, a search engine that focuses on the heritage of churches around the world.