An Italian Catholic priest in the Dominican Order a philos­opher and a theologian He was a proponent of natural theology. The work for which he is best-known is the Summa Theolo­gica. One of the 33 “Doctors of the Church”, he is considered by many to be the Catholic Church's greatest theologian and philos­opher. Based on reason and experience

There have been many attempts to prove the existence of God. If you had to debate an atheist, what would you say?

5.1.1. Prime mover; the umoved mover
5.1.1.1. Some things move.
5.1.1.2. Everything moving is moved by something.
5.1.1.3. An infinite regression of movement is impossible
5.1.1.4. Therefore, there must be an unmoved mover of everything else.
5.1.1.5. The unmoved mover is God.

5.1.2. Efficient cause
5.1.2.1. Some things are cuased
5.1.2.2. Everything caused is caused by something else
5.1.2.3. An infinite regression of cause is imposs­ible.
5.1.2.4. Therefore, there must be an uncaused cause of everything else.
5.1.2.5. The uncaused cause is God.

5.1.3. Contigency or being.
5.1.3.1. Some things exist and are contigent upon someone making the existence.
5.1.3.2. It is impossible for everything to be contigent, for then there would be a time when nothing existed; and so if there were nothing, nothing would exist now. That is, there is nothing to bring anything into existence. This is clearly false. Therefore, we have regressed contigency of existence back to God.

5.2. Perfect being
5.2.1. Varying degrees of perfection exist throughout the world
5.2.2. Varying degrees assume an ultimate standard of perfection
5.2.3. The ultimate standard of perfection is a supreme being, God.

5.3. Perfect design- the order of the univer­se.
5.3.1. All natural bodies of the world act toward ends (Laws of Physics, etc)
5.3.2. These objects of themselves are uninte­lligent
5.3.3. There must exist a supreme intell­igence that guides all natural bodies toward their end.
5.3.4. This intell­igence is God.