When I was in Catholic grammar school, one of the parish priests, Fr. Joyce, would visit our classroom periodically and teach for an hour. He had no prepared lesson plans that I knew of, but he loved philosophy and would sometimes teach us simplified bits of Aristotle and Thomas Aquinas. In the sixth grade, he told us that Aquinas had written five proofs of the existence of God which he wrote on the blackboard. When I read the proofs on the board, I said to myself, "No, they don't prove the existence of God to me." I believed in the existence of God without question, but these proofs didn't persuade me.
Note that Aquinas lived in the 1200s and wrote in Latin. When I was in my fifties, I had read an article that pointed out that the Latin word for proof was "prober," which means. "to probe." Aquinas was not so much as proving the existence of God but probing, that is, seeking. That insight makes all the difference. Aquinas was not attempting to "prove" the existence of God in a mathematically logical or scientific sense. In fact, Aquinas says that we cannot know God without Revelation. The same article claimed that the modern usage of the word "proof" was not used, or at least was not in common usage, until after Descartes and the Enlightenment in the late 1600s. As well, note that Aquinas did not call them Five Proofs but rather Five Ways. The Encyclopedia Britannica does not call them proofs but rather, demonstrations. The traditional Catholic claim of Aquinas "proving" the existence of God was an attempt to impose a post-Cartesian way of thinking on pre-Cartesian ideas.
I now appreciate the genius--the mystical genius--of Aquinas! He was exploring the Religious Sense. He was probing the infinite, the mysterious infinite. Suddenly, a doctrine which I first experienced as oppressive and authoritarian became a principle of light and freedom.
Of course, I have had no formal education in theology, much less Aquinas. The Wikipedia page (2018) for The Five Ways says, "Many scholars and commenters caution in treating the Five Ways as if they were modern logical proofs." It also says, "Aquinas did not think the finite human mind could know what God is directly; therefore, God's existence is not self-evident to us. So instead the proposition God exists must be "demonstrated"from God's effects, which are more known to us." This is not to say that examining them in that light is not academically interesting."
The Five Ways
1. the argument from motion
2. the argument from causation
3. the argument from contingency
4. the argument from degree
5. the argument from final cause or ends