Summary of the Five Ways

First Way

1. Evident to the senses is motion. (Premise)

2. Everything in motion has its motion sustained by another. (Premise)

3. Either an Unmoved Mover exists, or else there is an infinite regress of sustaining movers. (Implied by 1 and 2)

4. There cannot be an infinite regress of sustaining movers. (Premise)

5. Therefore, an Unmoved Mover exists. (From 3 and 4)


Second Way

1. Dependent things exist. (Premise)

2. Every dependent thing has a sustaining cause. (Premise)

3. Either an independent first cause exists, or else there is an infinite regress of dependent sustaining causes. (Implied by 1 and 2)

4. There cannot be an infinite regress of dependent sustaining causes. (Premise)

5. Therefore, an independent first cause exists in the order of sustaining causes. (From 3 and 4)


Third Way

1. Everything that exists is either necessary or contingent. (Definition)

2. Something presently exists. (Premise)

3. Something cannot come from nothing. (Premise)

4. Hence, there was never a past time at which nothing existed. (Implied by 2 and 3)

5. The past is infinite. (Assumption)

6. Given infinite time, all potentialities will have been actualized. (Premise)

7. The concurrent nonexistence of all contingent entities is a potentiality.

8. Hence, there was a past time at which nothing contingent existed. (From 6 and 7)

9. Therefore, a necessary entity exists. (From 1, 4 and 8)


Fourth Way

1. There are degrees of truth and goodness that possess limitations. (Premise)

2. Limitations can be known only in reference to a standard of perfect truth and goodness. (Premise)

3. Hence, there is a standard of perfect truth and goodness. (From 1 and 2)

4. Necessarily, a standard perfect truth and goodness will be the supreme object of desire. (Premise)

5. A supreme object of desire can only have the effects of desirability if it exists. (Premise)

6. Therefore, a supreme object of desire exists. (From 3, 4 and 5)


Fifth Way

1. Whatever exhibits regularity is the result of some entity's providence. (Premise)

2. Nature exhibits regularity. (Premise)

3. Therefore, nature is the result of some entity's providence. (From 1 and 2)