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