In the Summa Theologia I (STI), beginning at question 2, article 3, and in the Summa Contra Gentiles I (CGI), beginning at chapter 13, Aquinas provides five proofs for the existence of God. These proofs are intended to demonstrate that God exists and to provide the foundation for a larger program to demonstrate many other doctrines which are held by faith. However, the program which Aquinas sets up for himself in the two great Summae is trivial and unnecessary if the existence of God is self-evident in such a way that God's existence needs no demonstration. So, as a preamble to the five ways, Aquinas argues that the existence of God is not self-evident in any way that would hinder his program of rational theology.

In STI the argument occurs in question 2, article 1, and in CGI it occurs in chapters 10 and 11. Aquinas also argues the same point in Commentum in Primum Librum Sententiarum (CS) distinction 3, question 1, article 2, and in Quaestiones Disputate De Veritate (DV) question 10, article 12.