St Thomas Aquinas, the “Angelic Doctor”, was a Dominican friar, and the greatest of the medieval philosopher-theologians. Following his death, several of his views were condemned by the church. He soon increased in popularity, though, and in 1323 was canonised. To be canonised, one must have performed two authenticated miracles; the Pope judged St Thomas to have done so in resolving difficult questions of philosophical theology.

Aquinas’s final and greatest work, Summa Theologica, was left incomplete; he ceased all writing following a religious experience, explaining, “All that I have written seems to me like straw compared to what has now been revealed to me.” Even incomplete, however, the work is substantial, offering a comprehensive synthesis of Christian doctrine and the philosophy of Aristotle.

Aquinas held that God’s existence is not self-evident to us, rejecting Anselm’s ontological argument, and that it therefore requires demonstration. He sought to do this in his quinque viae or “Five Ways”, offering five arguments for the existence of God. The first three of these arguments are forms of cosmological argument, while the fifth is a teleological argument.